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Exposure to chronic hypoxic conditions causes various gastric diseases, including gastric ulcers. It has been suggested that gastric smooth muscle contraction is associated with aerobic metabolism. However, there are no reports on the association between gastric smooth muscle contraction and aerobic metabolism, and we have investigated this association in the present study. High K+- and carbachol (CCh)-induced muscle contractions involved increasing O2 consumption. Aeration with N2 (hypoxia) and NaCN significantly decreased high K+- and CCh-induced muscle contraction and O2 consumption. In addition, hypoxia and NaCN significantly decreased creatine phosphate (PCr) contents in the presence of high K+. Moreover, decrease in CCh-induced contraction and O2 consumption was greater than that of high K+. Our results suggest that hypoxia and NaCN inhibit high K+- and CCh-induced contractions in gastric fundus smooth muscles by decreasing O2 consumption and intracellular PCr content. However, the inhibition of CCh-induced muscle contraction was greater than that of high K+-induced muscle contraction.

The mechanism of imidazole-induced contraction on the bovine tracheal smooth muscle was investigated. Imidazole induced muscle contraction in a concentration-dependent manner on bovine, porcine and guinea-pig tracheas, but not in rat or mouse. In bovine tracheas, imidazole was cumulatively applied and induced muscle tension and increasesd intracellular Ca2+ level in a concentration -dependent manner. Imidazole, even at 300 µM, the concentration at which maximum contractile response occurs, did not significantly increase in cAMP content relative to control. Atropine inhibited imidazole-induced contraction at a concentration- dependent manner and pretreatment of hemicholinium-3 almost abolished imidazole-induced contraction. Conversely, pretreatment of tripelennamine, indomethacin or tetrodotoxin did not affect imidazole-induced contraction. Acetylcholine or eserine induced contraction in bovine, porcine, guinea pig, rat and mice trachea in a concentration-dependent manner. However, there was little difference in the rank order of maximum contraction of these agents. Imidazole-induced contraction was greater in bovine trachea compared to the other species tested. Further, cAMP did not appear to play a role in imidazole-induced contraction, suggesting other mechanisms, such as the release of endogenous acetylcholine.

Chlorogenic acid (CGA) is a polyphenol found in coffee and medicinal herbs such as Lonicera japonica. In this study, the effect of CGA-induced relaxation on carbachol (CCh)-induced contraction of mouse urinary bladder was investigated. CGA (30–300 μg/ml) inhibited CCh- or U46619-induced contraction in a concentration-dependent manner. SQ22536 (adenylyl cyclase inhibitor) recovered CGA-induced relaxation of CCh-induced contraction; however, ODQ (guanylyl cyclase inhibitor) did not have the same effect. In addition, 3-isobutyl-1-methylxanthine (IBMX) enhanced CGA-induced relaxation; however, forskolin or sodium nitroprusside did not have the same effect. Moreover, Ro 20–1724, a selective phosphodiesterase (PDE) 4 inhibitor, enhanced CGA-induced relaxation, but vardenafil, a selective PDE5 inhibitor, did not have the same effect. In the presence of CCh, CGA increased cyclic adenosine monophosphate (cAMP) level, whereas SQ22536 inhibited the increase of cAMP levels. Moreover, higher cAMP levels were obtained with CGA plus IBMX treatment than the total cAMP levels obtained with separate CGA and IBMX treatments. In conclusion, these results suggest that CGA inhibited CCh-induced contraction of mouse urinary bladder by partly increasing cAMP levels via adenylyl cyclase activation.

The present study was designed to clarify phosphodiesterase 9 (PDE9) expression in bovine tracheal smooth muscle tissue, and to elucidate that PDE9 may contribute to the regulation of airway relaxation. PDE9 mRNA expression was detected in bovine tracheal smooth muscle. Sodium nitroprusside (an NO donor) and BAY 73-6691 (a selective PDE9 inhibitor) reduced high K+- and carbachol-induced contraction. BAY 73-6691 relaxed tracheal tissue on the same level with vardenafil (a selective PDE5 inhibitor). These results support our hypothesis that PDE9 plays functional role in the tracheal smooth muscle relaxation. PDE9 inhibitors are expected to be a novel target of the add-on treatment of airway hyperresponsiveness.

Recent studies have shown that phloridzin, an inhibitor of sodium-glucose cotransporter (SGLT), strongly decreases high K+-induced contraction in phasic muscle, such as tenia coli, but slightly affects tonic muscle, such as trachea . In this study, we examined the inhibitory mechanism of phloridzin on high K+-induced muscle contraction in rat ileum, a phasic muscle. Phloridzin inhibited the high K+-induced contraction in the ileum and the aorta, and the relaxing effect of phloridzin at 1 mM in the ileum was approximately five-fold more potent than that in the aorta. The expression of SGLT1 mRNA in the ileum was higher than that of the aorta. Phloridzin significantly inhibited NADH/NAD ratio and phosphocreatine (PCr) content in the ileum; however, application of pyruvate recovered the inhibition of contraction and PCr content, but had no effect on ratio of NADH/NAD. High K+ increased 2-(N (7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-2-deoxyglucose (2-NBDG) uptake in ileal smooth muscle cells, and phloridzin inhibited the increase in a concentration-dependent manner. These results suggest that phloridzin inhibits high K+-induced contraction because of the inhibition of energy metabolism via the inhibition of SGLT1.

Eyes are supplied O2 through the cornea and vessels of the retina and iris, which are tissues characterized by aerobic metabolism. Meanwhile, there are no reports on the association between iris sphincter contraction and aerobic metabolism. In this paper, we studied the aforementioned association. Eyes from adult pigs of either sex were obtained from a local abattoir. A muscle strip was connected to a transducer to isometrically record the tension. O2 consumption was measured using a Clark-type polarograph connected to a biological oxygen monitor. Creatine phosphate (PCr) and adenosine triphosphate (ATP) contents were measured in the muscle strips by high-performance liquid chromatography (HPLC). Iris sphincter muscles were measured in resting, contractile or hypoxic phases. Contraction was induced by hyperosmotic 65 mM KCl (H-65K+) or carbachol (CCh), and hypoxia was induced by aeration with N2 instead of O2 or by addition of sodium cyanide (NaCN). H-65K+- and CCh-induced muscle contraction, involved increasing O2 consumption. Hypoxia and NaCN significantly decreased H-65K+- and CCh-induced muscle contraction and/or O2 consumption and PCr contents. Our results suggest that the contractile behavior in porcine iris sphincter highly depends on mitogen oxidative metabolism.

The effects of various selective phosphodiesterase (PDE) inhibitors on carbachol (CCh)-induced contraction in the bovine abomasum were investigated. Various selective PDE inhibitors, vinpocetine (type 1), erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, type 2), milrinone (type 3), Ro20-1724 (type 4), vardenafil (type 5), BRL-50481 (type 7) and BAY73-6691 (type 9), inhibited CCh-induced contractions in a concentration-dependent manner. Among the PDE inhibitors, Ro20-1724 and vardenafil induced more relaxation than the other inhibitors based on the data for the IC50 or maximum relaxation. In smooth muscle of the bovine abomasum, we showed the expression of PDE4B, 4C, 4D and 5 by RT-PCR analysis. In the presence of CCh, Ro20-1724 increased the cAMP content, but not the cGMP content. By contrast, vardenafil increased the cGMP content, but not the cAMP content. These results suggest that Ro20-1724-induced relaxation was correlated with cAMP and that vardenafil-induced relaxation was correlated with cGMP in the bovine abomasum. In conclusion, PDE4 and PDE5 are the enzymes involved in regulation of the relaxation associated with cAMP and cGMP, respectively, in the bovine abomasum.

The effects of papaverine on carbachol (CCh) -and high K+- induced contraction in the bovine abomasum were investigated. Papaverine inhibited CCh (1 µM) -and KCl (65 mM) -induced contractions in a concentration-dependent manner. Forskolin or sodium nitroprusside inhibited CCh-induced contractions in a concentration-dependent manner in association with increases in the cAMP or cGMP contents, whereas papaverine increased cGMP contents only at 30 µM. Changes in the extracellular Ca2+ from 1.5 mM to 7.5 mM reduced verapamil-induced relaxation in high K+-depolarized muscles, but papaverine-induced relaxation did not change. Futhermore, papaverine (30 µM) and NaCN (300 µM) decreased the creatine phosphate contents. These results suggest that the relaxing effects of papaverine on the bovine abomasum are mainly due to the inhibition of aerobic energy metabolism.

This study examined the inhibitory effects of papaverine on twitches directly elicited by electrical stimulation of the mouse diaphragm. Papaverine (3–100 µM) inhibited twitches in a dose-dependent manner. Papaverine increased the cyclic adenosine monophosphate (cAMP) but not cyclic guanosine monophosphate (cGMP) content. IBMX, Db-cAMP and 8-br-cGMP did not affect twitches, whereas verapamil and NaCN inhibited twitches. Increases in extracellular Ca2+ removed the twitch inhibition caused by verapamil but not that caused by papaverine. Papaverine (30 and 100 µM) and NaCN (1 mM) decreased creatine phosphate and ATP contents. These results suggest that the relaxing effects of papaverine on mouse diaphragm are mainly due to inhibition of aerobic energy metabolism.

A high-K(+), Na(+)-deficient (isosmotic 154 mM K(+) and 0 mM Na(+); I-154 K(+)) solution induced contraction followed by gradual relaxation of the smooth muscles of the porcine trachea, while hyperosmotic addition of 65 mM KCl (H-65 K(+)) induced a large sustained contraction. The I-154 K(+) solution also induced a sustained increase in [Ca(2+)](i) level. Decreases in muscle tension and increases in cellular water content were both prevented by the addition of sucrose or NaCl in the porcine trachea. An additional application of phloridzin inhibited recoveries of I-154 K(+) solution by addition of NaCl in the porcine trachea. Addition of pyruvate or oxaloacetate recovered the I-154 K(+) solution-induced relaxation in the porcine trachea. Although application of I-154 K(+) solution did not affect PCr and ATP contents in the bovine trachea, the solution induced a gradual decrease of PCr content in the porcine trachea. Moreover, application of pyruvate or oxaloacetate recovered the I-154 K(+) solution-induced decreases of PCr content in the porcine trachea. Phloridzin inhibited H-65 K(+)-induced contraction in porcine, but not in bovine trachea. In conclusion, the I-154 K(+) solution-induced relaxation in the porcine trachea is probably due to swelling of cells and inhibition of glucose utilization. Moreover, the inhibition of glucose utilization in I-154 K(+) medium in porcine trachea is different from that of bovine trachea.

This study examined the mechanism of vasorelaxation induced by dimethyl sulfoxide (DMSO) in endothelium-intact and -denuded rat aorta. DMSO (0.1-3%) inhibited phenylephrine (PE, 1 μmol/l)-induced contraction in a dose-dependent manner. However, this relaxation was lower in the absence of the endothelium. Increase in DMSO-induced relaxation in the presence of the endothelium was attenuated by preincubation in L-NG-nitroarginine methyl ester (L-NAME, 100 μmol/l) and by the removal of the endothelium. In the aorta with endothelium, DMSO (3%) and CCh (3 μmol/l) increased cGMP contents, significantly and L-NAME (100 μmol/l) inhibited the DMSO-induced increases of cGMP. In fura 2-loaded endothelium-denuded aorta, cumulative application of DMSO (1-3%) inhibited PE-induced muscle tension; however, this application did not affect the [Ca2+]i level. In PE-precontracted endothelium-denuded aorta, relaxation responses to fasudil were significantly less in the presence of DMSO compared to the control. These results suggest that DMSO causes relaxation by increasing the cGMP content in correlation with the release of NO from endothelial cells and by decreasing the Ca2+ sensitivity of contractile elements partly via inhibiting Rho-kinase in rat aorta.

We have demonstrated that the relaxing mechanism of papaverine in phasic muscles such as ileum, urinary bladder, and uterus is different from tonic muscles such as aorta. In this study, we examined the inhibitory mechanism of papaverine on carbachol (CCh)-induced contraction in the bovine trachea. Papaverine inhibited muscle contraction and increase in [Ca2+]i level induced by CCh. Papaverine increased cAMP content but not cGMP content. Papaverine did not affect CCh-induced oxidized flavoproteins fluorescence or reduced pyridine nucleotides fluorescence. Papaverine (30 µM) remarkably inhibited muscle tension, but slightly decreased creatine phosphate and ATP contents. Iberiotoxin restored the inhibitions of muscle contraction and [Ca2+]i level induced by papaverine or dibutyryl-cAMP. These results suggested that the relaxing mechanism of papaverine in the bovine trachea is mainly due to increases of cAMP content by inhibiting phosphodiesterase and the mechanism is partially involved in the activation of BK channel by cAMP. Keywords:: papaverine, bovine, trachea, cAMP, iberiotoxin

Effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in guinea pig taenia coli were investigated. Forskolin and sodium nitroprusside inhibited carbachol (CCh)-induced contraction in a concentration-dependent manner. Various selective PDE inhibitors, vinpocetine (type 1), erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20-1724(type 4) and zaprinast (type 5) inhibited CCh-induced contraction in a concentration-dependent manner, but the inhibition of milrinone was noticeably smaller than that of the other PDE inhibitors. The rank order of potency was zaprinast > vinpocetine > EHNA > Ro20-1724 > milrinone. In the presence of CCh (0.3 microM), vinpocetine and Ro20-1724 both increased cAMP content, but not cGMP. By contrast, EHNA and zaprinast both increased cGMP content, but not cAMP. Pretreatment with ODQ (30 microM), a soluble guanylyl cyclase inhibitor, decreased the inhibition of CCh-induced contraction by EHNA or zaprinast. Pretreatment with SQ22536 (100 microM), an adenylyl cyclase inhibitor, decreased the inhibition of CCh-induced contraction by vinpocetine or Ro20-1724. In conclusion, it was indicated that vinpocetine- or Ro20-1724-induced relaxation was correlated with cAMP but EHNA- or zaprinast- induced relaxation was correlated with cGMP.

The effects of the type V phosphodiesterase (PDE V) inhibitors, MBCQ, zaprinast and dipyridamole, on the relationship between relaxation and cyclic nucleotide content were investigated in rat ileal smooth muscle. Each of MBCQ (0.01-10 microM), zaprinast (0.1-100 microM) and dipyridamole (0.1-100 microM) inhibited carbachol (CCh; 10 microM)-induced contractions in a concentration-dependent manner. When compared with the concentrations of these agents producing 50% relaxation (IC50) of CCh-induced contraction, MBCQ was 14-20 fold more potent than the other agents. The inhibitory potency of these agents against high K+ (65 mM KCl)-induced contractions were similar to that for CCh. MBCQ (1, 10 microM) did not significantly increase the cGMP content above control levels in the presence of CCh (10 microM). Both Zaprinast (1-100 microM) and dipyridamole (1-100 microM) increased the cGMP content of smooth muscle preparations in a concentration-dependent manner. There was a positive correlation between the inhibition of the CCh-induced contraction and the increase in cGMP content elicited by zaprinast and dipyridamole (zaprinast; r=0.72, P0.05, dipyridamole; r=0.92, P0.05). However, MBCQ at a concentration which induced a medium-sized relaxation did not significantly increase the cGMP content. Neither MBCQ, zaprinast nor dipyridamole significantly increased the cAMP content of the preparations above control. In summary, it is suggested that the inhibition of CCh-induced contractions by zaprinast and dipyridamole involves increases in cGMP content via inhibition of PDE V. However the inhibition of CCh-induced contraction by MBCQ may not involve cyclic nucleotides in rat ileal smooth muscle.

In the present paper, we examined a mechanism of the papaverine induced relaxation in the smooth muscle of non-pregnant rat uterus. The hyperosmotic 65 mM KCl (H-65K+)-or oxytocin-induced contraction in the uterus was inhibited by an addition of papaverine in a concentration-dependent manner. Papaverine did not increase both cAMP and cGMP contents in the uterus in the presence of H-65K+ or oxytocin. In fura 2 loaded muscles, papaverine did not affect an increase of [Ca2+]i level by high K+ or oxytocin. In permeabilized muscles, papaverine had no effect on the Ca2+-induced contraction. H-65K+ and oxytocin increased the rate of oxygen consumption 1.8 and 1.5 times higher than that in the resting condition, respectively. The increase of oxygen consumption in the H-65K+ or oxytocin was significantly inhibited by papaverine (1-100 microM). These results suggested that papaverine inhibits smooth muscle contraction mainly by inhibition of mitochondrial respiration in rat uterus as well as guinea pig ileum, which shows a highly spontaneous activity and a highly metabolic dependency of a contraction.

Gymnema sylvestre (GS) is one of the Asclepiad strains that grows in South-east Asia. Their therapeutic effects for treating diabetes mellitus, rheumatic arthritis and gout have been well known for a long time. However, the problem is that GS suppresses sweetness and tastes bitter. For this study, we chose Gymnema inodorum (GI) instead of GS, since it has an advantage that it does not suppress sweetness nor is it bitter in taste. In this paper, effects of glucose availability of some saponin fractions (F-I to F-IV) extracted from GI leaves, which were obtained by high-performance liquid chromatography were studied on a high K(+)-induced contraction of guinea-pig intestinal smooth muscle, O2 consumption on guinea-pig ileum, glucose-evoked transmural potential difference (delta PD) of guinea-pig everted intestine and blood glucose level in glucose tolerance tests on rats. The extracts of GI leaves suppressed the intestinal smooth muscle contraction, decreased the O2 consumption, inhibited the glucose evoked-transmural potential, and prevented the blood glucose level. Our studies suggest that the component of GI inhibits the increase in the blood glucose level by interfering with the intestinal glucose absorption process.

Two substances identified as ((3 beta, 4 alpha, 16 beta, 21 beta, 22 alpha)-21-tigloxy-16, 22, 23, 28-tetrahydroxyolean-12-en-3-yl-beta D-glucopyranosiduronic acid) (GA1) and ((3 beta, 4 alpha, 16 beta, 21 beta, 22 alpha)-21-(2-methylbutyroxy)-16, 22, 23, 28-tetrahydroxyolean-12-en-3-yl-beta-D-glucopyranosiduronic acid) (GA2) identified among the gymnemic acids are triterpene glycosides extracted from Gymnema sylvestre leaves. We examined the effects of GA1 or GA2 on high K(+)-induced contraction in the guinea-pig longitudinal muscle. A sustained muscle contraction induced by hyperosmotically added 65.4 mM KCI (H-65K+) was suppressed by GA1 or GA2 (7.7 x 10(-5) M). Simultaneous measurements of reduced pyridine nucleotide (PNred) or oxidized flavin protein (FPox) by the fluorescence technique and of contractile force revealed that GA1 and GA2 reduced the increase of PNred fluorescence and contractile force induced by H-65K+, whereas FPox fluorescence induced by it further increased. Reduced muscle contraction induced by GA1 or GA2 was restored by 5.5 mM pyruvate. Simultaneous measurements of intracellular Ca2+ [Ca2+]1 level and contractile force indicated that [Ca2+]1 level, which increased by H-65K+, hardly changed with GA1 and GA2. In summary, both GA1 and GA2, which are among the gymnemic acids, suppressed high K(+)-induced contraction in the guinea-pig ileal longitudinal muscle. The difference between these two gymnemic acids was not significant. The inhibitory effect of GA1 and GA2 on smooth muscle were assumed to be a result of inhibiting glucose uptake, which is an energy source of the muscle, whereas the inhibitory mechanisms were probably not mediated by Ca2+.

Effects of phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPB), on muscle tension and cytosolic Ca2+ ([Ca2+]i) level was investigated in rat anococcygeus muscle in comparison with other smooth muscles. 1) DPB (10(-6) M) induced a large contraction and an elevation of [Ca2+]i level in rat aorta and small and rhythmic changes in tension and [Ca2+]i level in guinea pig ileum. However, DPB did not change either of the parameters in rat anococcygeus muscle. 2) DPB caused tension development without changing the [Ca2+]i level elevated by high K+, ionomycin or beta-escin in the anococcygeus muscle. 3) In the beta-escin permeabilized muscles of guinea pig ileum and urinary bladder, rabbit mesenteric artery and rat anococcygeus muscle, DPB enhanced the Ca(2+)-developed tension. Moreover, the enhancement was inhibited by H-7 (3 x 10(-5) M). 4) DPB did not cause muscle tension to develop in the muscle of rat aorta, guinea pig ileum and rat anococcygeus muscle, pretreated with phorbol 12-myristate 13-acetate for 24 hr. In conclusion, DPB showed different contractile effects on the aorta, ileum and anococcygeus muscle, respectively. The initiation of muscle tension by DPB probably requires [Ca2+]i and the DPB-induced enhancement may be due to a Ca2+ sensitization of contractile elements in the anococcygeus muscle. Therefore, the difference between the DPB-induced response of the anococcygeus muscle and those of the other muscles seems to be due to a different Ca2+ movement caused by DPB. Moreover, it is suggested that DPB develops muscle tension by increasing [Ca2+]i and enhances it through the mediation of protein kinase C in the anococcygeus muscle as well as the other smooth muscles.

The mechanism of the inhibitory effect of Li + on contraction was examined in guinea pig ileal longitudinal smooth muscle. Li + -substitution (68.4 mM) reversed contractions induced by high K + (45.4 mM), carbachol (1 μM) and histamine (1 μM) without changing the cytosolic Ca 2+ level. Li + also had no effect on the increase in 45 Ca 2+ uptake stimulated by high K + . High K + transiently increased myosin light chain (MLC) phosphorylation, reaching a peak at 6-9 sec. Li + -substitution inhibited the high K + -induced MLC phosphorylation. In permeabilized ileal strips, contraction induced by 1 μM Ca 2+ was inhibited by 10 mM Li + . The inhibitory effect was antagonized by increasing the concentration of Ca 2+ or calmodulin. In the permeabilized muscle in which MLC was previously thiophosphorylated with 1 mM ATPγS and 3 μM Ca 2+ , ATP induced contraction in Ca 2+ free buffer. Li + added during this contraction did not show an inhibitory effect. In contrast, when 30 mM Li + was added during the thiophosphorylation, the contraction induced by the subsequent addition of ATP was inhibited. Li + (30 mM) changed neither the rate of relaxation induced by removing external Ca 2+ in permeabilized muscle nor the rate of dephosphorylation of MLC induced by crude phosphatase extracted from the ileum. Li + (15 mM), on the other hand, inhibited the rate of phosphorylation of MLC caused by crude MLC kinase extracted from the ileum. Li + did not inhibit the calmodulin activity as measured with the (Ca 2+ +Mg 2+ )-ATPase activity of the erythrocyte membrane. These results suggest that the inhibitory effect of Li + on contractions is attributable to the inhibition of MLC kinase in guinea pig ileum

A contractile property of phenylephrine (PE), alpha 1 agonist, on rat anococcygeus muscle was compared with that on rat aorta by simultaneously measuring changes in intracellular Ca2+ ([Ca2+]i) level and muscle tension. (1) PE (0.1-30 microM) and high K+ induced a sustained increases in [Ca2+]i level and muscle tension of both the muscles. (2) An application of verapamil (10 microM) and EGTA (4 mM) decreased the PE- or high K(+)-increased tension and [Ca2+]i level in both the muscle, respectively. (3) A cumulative application of PE or high K+ to anococcygeus muscle and aorta exhibited a positive relationship between [Ca2+]i and developed tension. The developed tension by PE was greater than that by high K+ at the same level of [Ca2+]i only in the aorta. A difference of regression slopes in the relationship between [Ca2+]i level and muscle tension under PE- and high K(+)-treatments in aorta was significant, but that in anococcygeus muscle was not. (4) An application of PE to anococcygeus muscle in Ca2+ free medium elicited a small transient contractile tension and increase in [Ca2+]i level, but that to aorta showed a large and transient increase in both the parameters. (5) Phorbol ester, DPB (1 microM), did not affect muscle tension or [Ca2+]i level in anococcygeus muscle, but DPB induced greater increases in aorta. (6) An application of PE (10 microM) with GTP produced a left shift in the pCa-tension curve in the beta-escin-permeabilized fiber of the anococcygeus muscle. In summary, it is suggested that the sustained contraction induced by PE in anococcygeus muscle is involved with the increases in [Ca2+]i which is due to Ca2+ influx mediated by alpha 1 receptor, but scarcely to Ca2+ release from the intracellular storage, and that an increase in Ca2+ sensitivity to PE is found only in the permeabilized anococcygeus muscle. The Ca(2+)-independent contractile mechanism in PE response as seen in aorta is probably to be absent in anococcygeus muscle. Moreover, it seems that the effect of the drug acting protein kinase C on anococcygeus muscle is extremely lesser than that on aorta.

The effect of CV-3988, a platelet activating factor antagonist, in the treatment of endotoxic shock was evaluated from the changes in plasma 6-keto-PGF1 alpha and thromboxane B2 concentrations. The animals consisted of 10 beagle dogs anesthetized with pentobarbital sodium and divided into a treatment group (n = 5) and a control group (n = 5). Endotoxic shock was experimentally induced in both groups by intravenous administration of endotoxin (lipopolysaccharide, 3 mg/kg). The treatment group was intravenously given 10 mg/kg of CV-3988 for 10 min from immediately after endotoxin. Mean aortic pressure, cardiac output and urine volume were remarkably decreased after the administration of endotoxin to both groups. These parameters were higher after the administration of CV-3988, in the treatment group than in the control group. Furthermore, the increase in plasma 6-keto-PGF1 alpha and thromboxane B2 concentrations was significantly inhibited. These results suggest the effectiveness of CV-3988 in the treatment of endotoxic shock.

The therapeutic effect of ulinastatin (25,000 U/kg, i.v.) on endotoxin-induced shock was compared with that of methylprednisolone (30 mg/kg, i.v.) in 17 anesthetized dogs. Both of these drugs had almost the same tendency to improve the hemodynamics, arachidonate cascade metabolites and pulmonary surface activity. There was little difference between the effectiveness of ulinastatin and that of methylprednisolone. It was newly confirmed that the release of 6-keto-PGF1 alpha, thromboxane B2 and leukotriene B4, arachidonate cascade metabolites and chemical mediators associated with endotoxin-induced shock, were significantly (p < 0.01 and p < 0.05) decreased by ulinastatin in the same way as methylprednisolone. These results suggest that ulinastatin is as useful as methylprednisolone for the treatment of endotoxin-induced shock.

A shock model was experimentally produced by intravenous injection of a lethal dose (3 mg/kg) of endotoxin under general anesthesia induced by pentobarbital sodium using 7 beagles. The effect of this endotoxic shock on the reticuloendothelial function was investigated. The blood endotoxin concentration peaked immediately after administration and decreased subsequently. However, the value still remained on an increased level (1,051 pg/ml) even at 360 min after endotoxin treatment. The lipid emulsion test as an index of reticuloendothelial phagocytotic activity and the arterial ketone body ratio as an index of the energy charge in the liver decreased after endotoxin treatment and failed to recover during the experiment. Fibronectin, one of opsonic proteins, tended to decrease after injection of the endotoxin and was significantly (p < 0.01) low at 180 and 360 min compared with the value before injection of the endotoxin. These results suggested the depression of the reticuloendothelial function during endotoxin-induced shock.

Accuracy assessment was undertaken under varying hemodynamic conditions for a lung water volume measurement device which is based on the principle of a double indicator dilution method using heat and sodium ions. Changes in extravascular thermal volume were investigated in dogs with endotoxin-induced shock. The isoproterenol- or propranolol-induced changes in hemodynamics had no effect on the measurement. This confirmed the high accuracy of this measuring method. The measurement revealed a tendency for the extravascular thermal volume to gradually increase (p < 0.05) during endotoxin shock. This confirmed the gradual progression of pulmonary edema during endotoxin shock.

The effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide content in the porcine coronary artery were investigated. Various selective PDE inhibitors, vinpocetine (type 1), erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, type 2), milrinone (type 3), rolipram (type 4), Ro20-1724 (type 4), and zaprinast (type 5), inhibited U46619-induced contractions in a concentration-dependent manner. The rank order of potency for the porcine coronary artery was rolipram > Ro20-1724 >milrinone > vinpocetine > zaprinast > EHNA, which was different from that of both the porcine carotid artery and aorta. Rolipram inhibited the U46619-induced muscle tension with a decreased [Ca(2+)](i) level, but inhibited the high K(+)-induced contraction without a change in [Ca(2+)](i) level. Rolipram increased cAMP but not cGMP content. Iberiotoxin restored the inhibition of muscle tension and the [Ca(2+)](i) levels induced by rolipram. U46619 and caffeine induced a transient increase in the [Ca(2+)](i) levels in a Ca(2+)-free solution, but rolipram only inhibited the U46619-induced Ca(2+) transient. In conclusion, rolipram is the most potent inhibitor in the porcine coronary artery, but not in the carotid artery and aorta. Moreover it is suggested that the mechanism by which rolipram causes relaxation is due to a decrease in the [Ca(2+)](i) levels and of the Ca(2+) sensitivity of the contractile elements to cAMP.

The effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in porcine iris sphincter were investigated. Forskolin and sodium nitroprusside inhibited carbachol (CCh)-induced contraction in a concentration-dependent manner. Various selective PDE inhibitors, vinpocetine (type 1), erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20-1724 (type 4) and zaprinast (type 5), also inhibited CCh-induced contraction in a concentration-dependent manner. The rank order of potency of IC50 was zaprinast > Ro20-1724 > EHNA ≥ milrinone > vinpocetine. In the presence of CCh (0.3 μM), vinpocetine, milrinone and Ro20-1724 increased cAMP, but not cGMP, contents. In contrast, zaprinast and EHNA both increased cGMP, but not cAMP, contents. This indicates that vinpocetine-, milrinone- and Ro20-1724-induced relaxation is correlated with cAMP, while EHNA- and zaprinast- induced relaxation is correlated with cGMP in porcine iris sphincter.

Disorders of bone metabolism caused by resection of three quarters of the small bowel in rats were investigated biochemically and histomorphologically. Metabolic bone disorders developing 90 days after in 75%-distal-small-bowel resected rats were characterized by reduction in ash content of the femur and by the disappearance of the trabecular bone in tibial metaphysis. Biochemical studies showed significant decrease in serum Ca and 1,25-dihydroxyvitamin D concentrations in 75% distal small bowel resected rats. These data suggest that 75% distal small bowel resection impairs intestinal absorption of calcium and results in a negative calcium balance, which may contribute to the development of bone metabolic disorder in rats. On the other hand, 75% proximal small bowel resection causes no obvious metabolic bone disorders in rats, possibly because of the adaptation by the remaining part of the intestine.

Kamizaki, J., Shimizu, K., Nakajyo, S. and Urakawa, N. A change in inhibitory mechanism of Na+deficiency on high K+-induced contraction in rat uterus with the progress of pregnancy. Jpn. J. Smooth Muscle Res.In the present paper, effects of high K+/Na+deficient solution on the rat uterus with the progress of the pregnancy were examined on the mechanical response and wet weight. The progress of pregnancy was divided in four stages, early stage (Day 4 and 5 of pregnancy), middle stage (Day 8-10), late stage (Day 14 and 15) and end stage (Day 21). In the early stage muscle, an isosmotically substituted high K+/Na+ deficient (iso-154K+) solution induced a large contraction followed by a decrease in tension level, though a hyperosmotic KCl addition induced a large sustained contraction. Similar results were shown in muscles of the middle and late stages, However, a maximum tension level and a subsequent inhibition by the iso-154K+ solution in the end stage muscle were smaller than those of other stages. On the other hand, iso-154K+solution remarkably increased the relative cellular water content in the early or middle stage muscle, but moderately in the late or end stage one. In the muscle of all stages, a hyperosmotic addition of sucrose reversed the inhibition of muscle tension and the cell swelling by the iso-154K+ solution. Moreover, a substitution of more impermeable anion (C2H5COO-) for Cl-in the iso-154K+solution decreased the inhibition of the contraction in the early stage muscle, but increased it in the end stage one. Thesubstitution for Cl-with more permeable anion (NO3-or I-) produced a greater inhibition of contraction in all stage muscles. Moreover, a substitution of pyruvate or oxalacetate forglucose in iso-154K+solution did not affect the decreased tension in the early stage muscle, however, reversed the decreased tension in those after the middle stage. From these results, the decrease of the developed tension in the iso-154K+solution in the early stage muscle is probably due to cell swelling and those after the middle stages is probably caused by both the cell swelling and the inhibition of glucose utilization by Na+deficiency in the medium. The data suggest that the mechanism of the decrease in tension is probably transferred from cell swelling to inhibition of glucose utilization with the progress of pregnancy.

The mechanism by which ibudilast induces vasodilation was examined in isolated endothelium-denuded rat aorta. Ibudilast inhibited the contractions induced by phenylephrine (PE) and high K+ with decrease of [Ca2+]i level in a concentration-dependent manner, to the same degree. 3-Isobutyl-1-methylxanthine (IBMX) inhibited PE-induced contraction and [Ca2+]i level in a concentration-dependent manner, but it inhibited high K+-induced contraction without decrease of [Ca2+]i level. In comparison with IBMX, the increases of cAMP and cGMP contents in ibudilast were much smaller than that of muscle tension. Ibudilast did not inhibit 12-deoxyphorbol 13-isobutyrate (DPB)-induced contraction in the presence of verapamil. Treatment with 30 µM ibudilast inhibited the extracellularly added Ca2+-induced muscle tension and increases in [Ca2+]i level during high K+ depolarization. These results suggested that ibudilast inhibited PE- and high K+-induced muscle contractions mainly by the inhibition of [Ca2+]i level in endothelium-denuded rat aorta. Keywords:: ibudilast, smooth muscle, cAMP, cGMP, rat aorta

In this study, we examined the inhibitory mechanism of monensin on high K+-induced contraction in guinea-pig urinary bladder. The relaxant effect of monensin (0.001 – 10 µM) was more potent than those of NaCN (100 µM – 1 mM) and forskolin (3 – 10 µM). Monensin (0.1 µM), NaCN (300 µM), or forskolin (10 µM) inhibited high K+-induced contraction without decreasing [Ca2+]i level. Monensin and NaCN remarkably decreased creatine phosphate and ATP contents. Monensin and NaCN inhibited high K+-induced increases in flavoprotein fluorescence, which is involved in mitochondrial respiration. Forskolin increased cAMP content but monensin did not. Monensin increased Na+ content at 10 µM but not at 0.1 µM that induced maximum relaxation. In the α-toxin-permeabilized muscle, forskolin significantly inhibited the Ca2+-induced contraction, but monensin did not affect it. These results suggest that the relaxation mechanism of monensin in smooth muscle of urinary bladder may be an inhibition of oxidative metabolism. Keywords:: monensin, urinary bladder, phosphocreatine, Na+ content

The leaves of Gymnema inodorum (GI) have been known to be effective for some diseases including diabetes mellitus, rheumatic arthritis and gout. The crude saponin mixtures extracted from GI leaves inhibited glucose absorption in the isolated intestinal tract and suppressed the increased blood glucose in rats. In this study, we examined the relationship between chemical structure and pharmacological activity of the four components from GI leave extracts (GiA-1, GiA-2, GiA-5 and GiA-7). These components were the derivatives of (3beta,4alpha,16beta)-16,23,28-trihydroxyolean-12-en-3-yl-beta-D-glucopyranosiduroic acid. GiA-2, GiA-5 and GiA-7 that have suppressive effects on the high K+-induced contraction, an increase in deltaPD and the increased blood glucose level in the glucose tolerance test have -H at the 21st position and -CH2OH at 4beta of aglycon. On the other hand, GiA-1 that does not have any effects on the three parameters mentioned above has -H at the 21st position and -CH3 at 4beta of aglycon. In conclusion, it is suggested that the inhibitory effect of triterpenoids in Gymnema leaves on glucose absorption from the intestinal tract relies on -CH2OH at 4beta.

In guinea pig urinary bladder, the hyperosmotic 65 mM KC1 (H-65K+)- or carbachol (CCh)-induced contraction was inhibited by an addition of papaverine in a concentration-dependent manner. The cAMP content of the muscle in the presence of H-65K+ or CCh was increased by papaverine only at the higher concentration of 100 μM, but cGMP content was not affected by papaverine. Forskolin, compared with papaverine, increased cAMP content in a concentration-dependent manner, and nitroprusside did not significantly increase cGMP content. In a fura 2 loaded muscle, papaverine did not affect an increase of [Ca2+]i level by high K+ or CCh. The increase of oxidized flavoprotein (FPox) fluorescence and muscle contraction in the presence of H-65K+ or CCh was decreased by papaverine (l-00 μM), and the increase of pyridine nucleotide (PNred) fluorescence was not affected by papaverine. In summary, it was concluded that papaverine induced relaxation by inhibiting mitochondrial respiration in guinea pig urinary bladder as well as ileum. Moreover, it is proposed that the mechanism of papaverine-induced relaxation in the smooth muscle, which shows predominantly a metabolic dependency on its contraction, is an inhibition of mitochondrial respiration.

The effect of TCV-309, a newly developed platelet activating factor (PAF) antagonist, on the wet/dry weight ratio of the lung (index of pulmonary edema) and the pulmonary surface activity (index of pulmonary compliance) was evaluated in comparison with that of CV-3988 (PAF-antagonist). Administration of TCV-309 (1 mg/kg) or CV-3988 (10 mg/kg) significantly reduced the wet/dry weight ratio which was increased by endotoxin administration (3 mg/kg). It also augmented the pulmonary surface activity. Administration of either TCV-309 or CV-3988 alleviated the histologic lesions caused by endotoxic shock. These results suggest that lung injury during endotoxic shock can be controlled by TCV-309 as by CV-3988.

The therapeutic effect of dibutyryl cyclic AMP (DBcAMP) in endotoxic shock was evaluated, using 11 dogs with experimentally-induced endotoxic shock (5 in DBcAMP group and 6 in control group) under general anesthesia. The DBcAMP group was treated by single intravenous injection of DBcAMP (10 mg/kg) at 15 min before inoculation with endotoxin (3 mg/kg). After the inoculation of endotoxin, this group was given drip infusion of DBcAMP at a rate of 0.1 mg/kg/min over 180 min. Hemodynamic parameters and chemical mediators were measured until 360 min after endotoxin inoculation. The cardiac output and urinary volume, which were decreased in the control group, were significantly inhibited to decrease in the DBcAMP group (p < 0.01). The increases in 6-keto-PGF1 alpha and thromboxane B2, chemical mediators released in endotoxic shock, were significantly inhibited (P < 0.05 and p < 0.01, respectively). These results suggested that DBcAMP is useful for the treatment of endotoxic shock.

The inhibitory effect of tiamulin, an antibiotic produced by Pleurotus mutilis, on contractile and electrical responses in isolated thoracic aorta and cardiac muscle of guinea-pigs was studied. In the thoracic aorta, tiamulin with an IC50 of 9·7 × 10−6 m inhibited sustained contractions induced by isosmotically added 60 Mm KCl. The inhibitory effect of tiamulin on a Ca2+-induced contraction in a depolarized muscle was competitively antagonized by raising external Ca2+ concentration. Bay K 8644 (10−7 m) antagonized tiamulin's inhibition of the Ca2+ -induced contraction. Tiamulin (2×10−5 m) decreased the elevated cytoplasmic Ca2+ level measured by the fura 2 AM method in the depolarized muscle. In high K+-isoprenaline-treated left atria, tiamulin (2 × 10−5–2 × 10−4 m) produced negative inotropic effects. On the other hand in the membrane action potential of papillary muscles, tiamulin (2 × 10−6–2 × 10−4 m) produced decreases in action potential and durations and 2 × 10−4 m tiamulin depressed the slow response action potential in depolarized muscles. Tiamulin produced prolongations of the PR interval in ECG, negative chrono- and inotropic effects, and an increase in perfusion flow in guinea-pig isolated and perfused hearts. These effects of tiamulin on the aorta or cardiac muscle were similar to those of verapamil and nifedipine. These results suggest that both the inhibitory action of tiamulin on the high K+-induced contraction in the aorta and the negative inotropic effect of tiamulin on the cardiac muscle are due to an inhibition of Ca2+ entry through the voltage-dependent Ca2+ channels of cells of both these muscles.

The mechanism of endothelium-dependent relaxation induced by pirarubicin, (2″R)-4′-O-tetrahydropyranyladriamycin, THP, or carbachol was investigated in the rat isolated aorta. The relaxant effect of THP (1·5 × 10−6-4·5 × 10−5 m) or carbachol (10−8-10−4 m) on the aorta with endothelium was decreased by lowering Ca2+ in the medium. The relaxation induced by THP was not inhibited by pretreatment with verapamil (10−6–10−5 m), and that induced by carbachol was only partially inhibited. However, on replacement of all but 20 Mm Na+ with either Li+ or choline, the THP- or carbachol-induced relaxation was inhibited. Furthermore, the relaxing effect of THP or carbachol was inhibited by pretreatment with amiloride (10−4-3 × 10−4 m), with ouabain (10−4-10−3 m), or with K+-depletion. These results suggest that the THP- or carbachol-induced relaxation depending on endothelium was affected by modifying the calcium ion concentration, and that a Na+–Ca2+ exchange process is involved.

The mechanism of relaxation produced by pirarubicin [(2″R)-4′-O-tetrahydropyranyladriamycin, THP] has been studied in rat isolated aorta. THP (1·5 × 10−6–4·5 × 10−5 m) markedly relaxed contractions induced by noradrenaline (10−7 m) in the aorta with endothelium, but not in that without endothelium. The relaxation induced by 1·5 × 10−5 m THP was inhibited by methylene blue (5 × 10−6 m), hydroquinone (10−4 m), phenidone (5 × 10−5 m), haemoglobin (10−6 m) and p-bromophenacyl bromide (5×10−5 m), but not by indomethacin (2·5 ×10−5 m). The relaxation induced by THP (1·5 × 10−7 − 4·5 × 10−5 m) was inhibited by NG-nitro-l-arginine (10−5 m), but enhanced by superoxide dismutase (10 units mL−1) or by L-arginine (10−2 m). However, the THP-induced relaxation was not inhibited by various receptor antagonists such as atropine (10−6 m), cimetidine (10−5 m), diphenhydramine (3 × 10−6 m) and [D-Pro4, D-Trp7,9,10]-substance P(4–11) (1·5 × 10−6 m). In fifteen anthracycline analogues, THP and 13-dihydropirarubicin (both with a tetrahydropyranyl group) produced endothelium-dependent relaxations. These results suggest that the THP-induced relaxation which is probably mediated by endothelium-derived relaxing factor (EDRF) was not produced by an activation of muscarine, histamine H1 or H2, or substance P receptor, and further that the tetrahydropyranyl group must play an important role in the THP-induced relaxation.

The effects of several organic Ca antagonists and putative calmodulin antagonists on the release of [ 3 H]noradrenaline from rabbit aorta were examined. A 65.4 mM K solution and electrical stimulation induced a Ca-dependent increase in the 3 H-efflux from the adventitial layer (containing nerve terminals) but not from the media-intimal layer. Verapamil, D600, N-(6-aminohexyl)-5-chloro-l-naphthalenesulphonamide (W-7) and N 2 -dansyl-L-arginine-4-t-butylpiperidine amide (TI 233), in the concentration of 10 −5 M, did not inhibit the increase in 3 H-efflux. A high concentration (2 × 10 −4 M) of verapamil induced a Ca-independent increase in the 3 H-efflux from the adventitia but not from the media-intimal layer. D600, diltiazem, W-7 and TI233, in the concentration of 2 × 10 −4 M, also increased the 3 H-efflux; 65.4 mM K, added in the presence of 2 × 10 −4 M verapamil or W-7, produced no further increase in 3 H-efflux. The 3 H-efflux evoked by electrical stimulation was only partially inhibited by 2 × 10 −4 M verapamil. It is suggested that the evoked release of noradrenaline in rabbit aorta is relatively insensitive to organic Ca antagonists and calmodulin antagonists, and that high concentrations of these inhibitors themselves release noradrenaline by a mechanism independent of external Ca.

The effect of caffeine on contractile activity and Ca movement was investigated in guinuEa pig taenia coll. Caffeine at a concentration of 7 mM produced a contraction for approx. 7 min and increased 45Ca influx and efflux without a change in Ca content in the tissue. The effect of caffeine on Ca movement was the same as that of carbachol in the early phase of the contractile response. The caffeine-contraction was not potentiated by an addition of Ca up to four times that of normal concentration, however, the carbachol-contraction was potentiated. When the muscle was soaked in a Ca-free solution, it showed “Ca-free contraction” and a loss of the tissue Ca content. When caffeine was added immediately after the “Ca-free contraction” was relaxed, caffeine produced a transient contraction and increased the loss of the tissue Ca content. Under identical circumstances, carbachol did not induce a contraction or affect the Ca content of the tissue. In conclusion, caffeine was demonstrated to increase Ca exchangeability in smooth muscle cell as did carbachol, however, the results suggested the possibility that caffeine releases a bound Ca in the cell for contraction whereas carbachol induces a contraction by an increase in a permeability of the cell membrane to Ca ions.

Tissue and cellular Na and K contents in aorta from spontaneously hypertensive rats were measured after long-term blockade of angiotensin converting enzyme with captopril. Cellular ion content was measured as a fraction after incubation in cold Li-solution. Tissue and cellular Na and K contents were lowered by 6 weeks treatment with captopril. Cellular Na or K loss in cold Li-solution was significantly slower in captopril-treated aortas. It is suggested that prolonged dosing of captopril decreases the leakiness of vascular muscle membrane and that this effect may contribute to the antihypertensive action of captopril.

1. The effects of procaine on muscle tension and 45Ca2+ movements were investigated in vascular smooth muscle of the rabbit aorta and intestinal smooth muscle of the taenia isolated from guinea-pig caecum. 2. Procaine (10 mM) induced a contraction in the taenia but had little effect on the resting tension in the aorta. 3. Procaine, 0.5-10 mM, relaxed the sustained contractions induced by 65.4 mM KCl and 10(-6) M noradrenaline in the aorta, and by 45.4 mM KCl, 10(-6) M carbachol and 10(-6) M histamine in the taenia. The inhibitory effect of procaine on the high K+-induced contractions was antagonized by external Ca2+ but not by the Ca2+ channel activators, Bay K 8644 and CGP 28,392. 4. 45Ca2+ uptake was increased by high K+ or noradrenaline in the aorta and by high K+ or carbachol in the taenia. The increments were inhibited by procaine at the concentrations needed to inhibit the muscle contractions. 5. In a Ca2+-free solution, noradrenaline and caffeine induced a transient contraction in the aorta, whereas a second application of each stimulant was almost ineffective. Addition of 1-10 mM procaine shortly before the first application of the stimulant inhibited the contraction. After washing the muscle with a Ca2+-free solution without procaine, the second application of the stimulant induced a greater contraction than that in control muscle without procaine pretreatment. 6. Noradrenaline and caffeine released 45Ca2+ from a cellular site in the aorta. Procaine inhibited the effects of these stimulants. 7. It was concluded that procaine may inhibit both the opening of Ca2+ channels and the release of Ca2 + from cellular stores and the former but not the latter effect may be attributable to a local anaesthetic action.

1. In guinea-pig aorta, K free solution and ouabain (2×10−5 M) produced sustained contractions with similar time course and magnitude. They were only partially inhibited by phentolamine (10−6 M). Experiments were conducted to investigate the mechanisms of these contractions. 2. When K was replenished after tension had reached a maximum in K free solution, the muscle strip slowly relaxed. Rb and Cs ions also diminished the contractions in K free solution and the order of effectiveness was K>Rb>Cs. The relaxation induced by these monovalent cations was inhibited by ouabain (2×10−5 M). 3. Contractions induced by K free solution and ouabain depended on the ratio [Ca]o/[Na]o/2; as long as the ratio [Ca]o/[Na]o/2was kept constant, the magnitude of the contractions did not change even if [Ca]o was lowered. 4. In low Na medium (11.9 mM), K depletion was ineffective and ouabain produced only a small contraction. 5. In K free solution or in the presence of ouabain, the muscle strips gained Na and lost K. The contraction started to develop when [Na]i was 70 mM/kg cell in K free solution or 50 mM/kg cell in 2×10−5 M ouabainsolution and reached its maximum when [Na]i was 85 mM/kg cell in both solutions. 6. The results suggest that these contractions are produced through a Na−Ca exchange mechanism following the accumulation of Na either by K free solution or by ouabain. Furthermore, ouabain seems to have an additive effect on the vascular tone.

The effects of verapamil and sodium nitroprusside on muscle tension and 45Ca uptake activated in different ways were compared in rabbit aorta, rat aorta and guinea-pig taenia coli. In rabbit aorta, K-induced contraction was specifically inhibited by verapamil and noradrenaline-induced contraction by sodium nitroprusside. In rat aorta, both K-induced and noradrenaline-induced contractions were inhibited by verapamil or by sodium nitroprusside also. In taenia, both K- and histamine-induced sustained contractions were inhibited by verapamil but not by sodium nitroprusside. The effect of verapamil was competitively antagonized by external Ca, while that of sodium nitroprusside was not. High K, noradrenaline and histamine increased the rate of 45Ca uptake in aortae and taenia. In rabbit aorta the increment in response to high K was specifically inhibited by verapamil and the increment induced by noradrenaline was specifically inhibited by sodium nitroprusside. In rat aorta, increments induced by both high K and noradrenaline were inhibited by verapamil and by sodium nitroprusside. In taenia, the increments induced by high K and by histamine were inhibited by verapamil but not by sodium nitroprusside. These results suggest different characteristics of Ca entry systems in these smooth muscles. In rabbit aorta, there seem to be two Ca channels, one of which is activated by high K and inhibited by verapamil, while the other is activated by noradrenaline and inhibited by sodium nitroprusside. In rat aorta, both K- and noradrenaline-activated Ca pathways are sensitive to both verapamil and sodium nitroprusside whereas, in taenia, both K- and histamine-activated Ca pathways are sensitive only to verapamil.

Ueda, F., Kishimoto, T., Karaki, H. and Urakawa, N. High K-induced Contraction in Rabbit and Monkey Tracheal Smooth Muscle. Jap.J. Smooth Muscle Res., 1983, 19 (6), 541-549. - High K-induced contractions in rabbit and monkey tracheal smooth muscle were characterized. A substituted 60mM K, 94.1mM Na solution produced a sustained contraction in both preparations. The 60 mM K-induced contraction in rabbit trachea was inhibited by Ca removal, verapamil, glucose-removal and hypoxia but not by sodium nitroprusside. The 60mM K-induced contraction in monkey trachea was inhibited by Ca removal, verapamil, sodium nitroprusside and hypoxia but not by glucose-removal. In rabbit trachea a substituted 154.1mMK, Na deficient solution induced a rapid rise in tension followed by a gradual decrease. Wet weight of rabbit trachea increased in the 154.1mM K solution. Both the decrease in the developed tension and the increase in the wet weight were prevented by the hyperosmotic addition of sucrose (50-100mM). The decrease in the developed tenison was also partially antagonized by the addition of pyruvate or oxalacetate. In monkey trachea, the sustained contraction induced by the 154.1mM K solution showed very slow decrease following the increase in the wet weight of the tissue. The decrease in muscle tension was prevented by the addition of hyperosmotic sucrose. These results suggest that, in rabbit tracheal smooth muscle, the decrease in the developed tension in isosmotically substituted high K, N a deficient solution may be attributable mainly to the swelling of muscle cells and partly to the inhibition of glucose utilization resulting from Na deficiency. In contrast, the contraction in monkey trachea seems to be inhibited, although slightly, by the swelling of the cells.

Nitroglycerine induced biphasic relaxation in the rat aorta, previously contracted by noradrenaline; a rapid decrease in tension was followed by a gradual increase reaching a steady level below the control contractile tension. No initial transient relaxation was induced by nitroglycerine in high K-stimulated muscle. The initial transient relaxation, but not the sustained relaxation, was dependent on the concentration of external K; maximum relaxation was observed in the presence of 2.7 mM K solution and only a slight relaxation was observed in 0 mM or 10.8 mM K solution. The initial transient relaxation was also inhibited by ouabain or low Na solution. On an appropriate increase in the concentration of external K, noradrenaline-induced contraction was transiently relaxed. Previous application of nitroglycerine potentiated this K-induced relaxation. Pretreatment of the muscle with methylene blue, an inhibitor of guanylate cyclase, inhibited both the initial transient and the sustained relaxations induced by nitroglycerine, but not the K-induced transient relaxation. It is suggested that the nitroglycerine-induced initial transient relaxation, but not the sustained relaxation, may be due to a stimulation of an electrogenic Na pump. Both relaxation phases may be mediated by cyclic GMP.