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Aims/hypothesis Sulfonylureas and glinides close beta cell ATP-sensitive K+ (KATP) channels to increase insulin release; the concomitant closure of cardiovascular KATP channels, however, leads to complications in patients with cardiac ischaemia. The insulinotrope repaglinide is successful in therapy, but has been reported to inhibit the recombinant KATP channels of beta cells, cardiocytes and non-vascular smooth muscle cells with similar potencies, suggesting that the (patho-)physiological role of the cardiovascular KATP channels may be overstated. We therefore re-examined repaglinide's potency at and affinity for the recombinant pancreatic, myocardial and vascular KATP channels in comparison with glibenclamide. Methods KATP channel subunits (i.e. inwardly rectifying K+ channels [Kir6.x] and sulfonylurea receptors [SURx]) were expressed in intact human embryonic kidney cells and assayed in whole-cell patch-clamp and [³H]glibenclamide binding experiments at 37°C. Results Repaglinide and glibenclamide, respectively, were ≥30 and ≥1,000 times more potent in closing the pancreatic than the cardiovascular channels and they did not lead to complete inhibition of the myocardial channel. Binding assays showed that the selectivity of glibenclamide was essentially based on high affinity for the pancreatic SUR, whereas binding of repaglinide to the SUR subtypes was rather non-selective. After coexpression with Kir6.x to form the assembled channels, however, the affinity of the pancreatic channel for repaglinide was increased 130-fold, an effect much larger than with the cardiovascular channels. This selective effect of coexpression depended on the piperidino substituent in repaglinide. Conclusions/interpretation Repaglinide and glibenclamide show higher potency and efficacy in inhibiting the pancreatic than the cardiovascular KATP channels, thus supporting their clinical use. [ABSTRACT FROM AUTHOR]

The effects of minoxidil sulphate, an "atypical" KATP channel opener, and bimakalim, a benzopyran-type classical KATP channel opener, on guinea pig airways in vitro and in vivo and on isolated portal veins from rats and guinea pigs were compared. Minoxidil sulphate inhibited the spontaneous activity of isolated guinea pig and rat portal vein preparations with pD2 values of 7.83±0.08 and 7.14±0.03, respectively (Emax=100% in both preparations). Bimakalim caused a more potent inhibition with pD2 values of 8.80±0.05 and 8.20±0.04, respectively (Emax=100% in both preparations). Minoxidil sulphate reduced the spontaneous tone of isolated guinea pig tracheal rings with a pIC50 value of 3.92±0.02 and the same efficacy as isoprenaline. Bimakalim was more potent (pIC50=7.25±0.02) but less efficacious (Emax=75% of the Emax of isoprenaline). The airway relaxant effect of bimakalim, but not minoxidil sulphate, was antagonised by glibenclamide (pA2=7.50) at concentrations above 0.1 µM. Bombesin-induced bronchoconstriction in anaesthetised, ventilated, normoreactive guinea pigs (measured as increase in total lung resistance) was dose-dependently reversed by intratracheally (i.t.) administered bimakalim (ED50=4 µg/kg; Emax=92% of maximally possible inhibition), but not by minoxidil sulphate, at doses up to 1 mg/kg i.t. In the same animals, following i.t. administration of higher doses, both minoxidil sulphate and bimakalim reduced blood pressure. Airways hyperreactivity to histamine induced by acute treatment of guinea pigs with immune complex was dose-dependently reversed by bimakalim (ED50=0.5 µg/kg i.t., Emax=100%). This effect was antagonised by glibenclamide (30 mg/kg i.v.). Minoxidil sulphate had a biphasic effect on airways hyperreactivity: at 1 µg/kg i.t., airways hyperreactivity was augmented, whereas at doses above 3.2 µg/kg i.t. it caused reversal of airways hyperreactivity. Both of the effects of minoxidil sulphate were insensitive to glibenclamide (30 mg/kg i.v.). It is concluded that the pharmacological profile of minoxidil sulphate in guinea pig airways is completely different from that of classical KATP channel openers such as bimakalim. Minoxidil sulphate is either only weakly active or even inactive at KATP channels in guinea pig airways or interacts with these channels in a different manner. The current results are consistent with there being differences between the KATP channels in airways and blood vessels. [ABSTRACT FROM AUTHOR]

Copyright of Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

After phosphorylation by protein kinase A and in the presence of ATP, the cystic fibrosis transmembrane conductance regulator (CFTR) functions as a Cl– channel. In this study we have examined the effects of suramin on the CFTR Cl– current (ICFTR) in excised inside-out macropatches from Xenopus oocytes expressing human CFTR; glibenclamide, the standard inhibitor of ICFTR, and some congeners were tested in comparison. ICFTR was activated by addition of the catalytic subunit of protein kinase A and MgATP to the bath. Suramin inhibited ICFTR with an IC50 value of 1 µM and a Hill coefficient close to 1; the inhibition showed little voltage dependence and was easily reversed upon washout of the drug. In comparison, glibenclamide inhibited ICFTR with an IC50 value of ≈20 µM. When tested against ICFTR in whole oocytes, bath application of suramin was ineffective whereas glibenclamide was about four times weaker than in the inside-out patch configuration. The data show that suramin is the most potent inhibitor of CFTR yet described and suggest that the compound approaches its site of action from the cytosol. [ABSTRACT FROM AUTHOR]

The cromakalim-induced effluxes of K and Rb were compared in rat aortic segments and in guinea-pig portal vein. In both vessels, low concentrations of cromakalim (0.1 μM) increased the permeability to Rb 3-4 times less than that to K; at 10 μM the difference was about a factor of 1.3-2. In rat aorta, the threshold concentration of cromakalim for K efflux was ≥0.03 μM; with Rb as the tracer ion it was 0.1 μM. At similar concentrations, cromakalim relaxed the tension of aortic segments precontracted with 23 mM KCl (IC = 0.06 ± 0.01 μM). However, no concomitant increase in K or Rb efflux could be detected from this stimulated preparation at these concentrations. In guinea-pig portal vein, K efflux measurements were performed in the presence and absence of the dihydropyridine Ca entry blocker PN 200-110 (isradipine) yielding comparable results. In the presence of PN 200-110, where spontaneous activity and the K efflux associated with it were abolished, the threshold concentration of cromakalim for K efflux was 0.02 μM as compared to 0.06 μM for Rb efflux. In the absence of PN 200-110, spontaneous activity of the portal vein was inhibited by 70% and 90% at these concentrations. In double isotope experiments, the K channel inhibitor tetraethylammonium did not discriminate between the effluxes of K and Rb stimulated by cromakalim. It is concluded that in the two vascular tissues examined, cromakalim increased the permeability to K more than to Rb, the difference being more marked at low cromakalim concentrations. The use of K as the tracer ion narrows the apparent gap between the concentrations of cromakalim which elicit vasorelaxant effects and those which induce an observable increase in K permeability; however a significant difference persists. [ABSTRACT FROM AUTHOR]

The experiments were undertaken to determine whether the effects of the K channel opener BRL 34915 on rat isolated vascular smooth muscle and atria were sensitive to pertussis toxin (PTx). PTx treatment of rats (100 μg/kg, infused over 15 min) affected some baseline parameters of the isolated tissues: in the atria, heart rate was increased, contractile force was decreased and the basal efflux of Rb was increased; in portal veins, the spontaneous activity was decreased but the contractility of aortic rings was unaffected. In the isolated atria removed from saline-treated rats, carbamylcholine decreased heart rate and contractile force, shortened the action potential duration by increasing the maximum rate of repolarization and increased Rb efflux. These effects of carbamylcholine were completely abolished in the atria from PTx-treated rats, demonstrating the efficacy of the toxin. The ability of 300 μM BRL 34915 and of 55 mM KCl to increase atrial Rb permeability was, however, only slightly affected by PTx treatment. In portal veins from PTx-treated rats, the efficacy of BRL 34915 to inhibit spontaneous activity and to increase Rb efflux was the same as in control organs. Similarly, in aortic rings, the ability of BRL 34915 to inhibit contractions to low concentrations of KCl or to noradrenaline was unaffected by PTx treatment as was the Rb efflux response to BRL 34915 in this tissue. It is concluded that PTx treatment does not inhibit the effects of BRL 34915 in the tissues investigated. The results are compatible with the notion that BRL 34915 does not open K channels by acting through a PTx-sensititive G-protein. [ABSTRACT FROM AUTHOR]

The in vitro cardiac effects of DPI 201-106, a novel piperazinyl-indole, were investigated. DPI 201-106 produced concentration-dependent positive inotropic effects in guinea-pig and rat left atria, kitten, rabbit and guinea-pig papillary muscles and Langendorff perfused hearts of rabbits between 10 and 3×10 mol/l. During isometric twitches, contraction and relaxation phases were prolonged in guinea-pig left atria and right ventricular papillary muscles from kitten and guinea-pigs. Spontaneous sinus rate was decreased in right atria of guinea-pigs and rats. Coronary flow increased in rabbit isolated hearts. Functional refractory period was increased in left atria from guinea-pigs and rats with EC values of 1.7 and 0.24 μmol/l respectively. In electrophysiological measurements, DPI 201-106 prolonged the action potential duration (APD) in guinea-pig papillary muscles up to 70% and in rabbit atria up to 120% at 3 μmol/l. Other action potential characteristics were not changed in guinea-pig papillary muscles but V was decreased in rabbit left atria. The electrophysiological as well as the positive inotropic effects were stereoselective with the activity residing in the S-enantiomer. DPI 201-106 increased the Ca-sensitivity of skinned fibres from porcine trabecular septomarginalis with an EC of 0.2 nmol/l. DPI 201-106 did not change cAMP levels in guinea-pig atria and rabbit papillary muscles. Slow action potentials were not induced by DPI 201-106 in partially depolarized guinea-pig papillary muscles. Phosphodiesterase activity of rat hearts was not inhibited by DPI 201-106 at pharmacologically relevant concentrations. The presence of propranolol did not influence the inotropic potency of DPI 201-106 in guinea-pig atria. In conclusion, DPI 201-106 represents a novel type of positive inotropic agents with a synergistic sarcolemmal and intracellular mechanism of action. [ABSTRACT FROM AUTHOR]

Data collected over a 15-year period concerning the side effects directly reported following administration of Tetanol were evaluated and it was found that the tetanus vaccination exhibited an extremely high degree of tolerance, with only 27 cases of side effects for 1 million doses. In over 80% of those cases with side effects the intolerance took the form of a painful reddening and/or swelling at the site of injection. This reaction to the vaccination, though not uncommon, was thus greater than is to be expected. General reactions, particularly malaise and an increase in body temperature, accounted for 10% of the cases reported; 3% involved skin reactions beyond the injection site. Symptoms involving the cardiac, circulatory, respiratory, locomotor, or nervous system occurred in fewer than 3 cases per 1 million doses, i.e., in fewer than 5% of the reported cases. It proved highly improbable that an allergic-anaphylactic or anaphylactoid reaction was involved and the complete picture of anaphylactic shock was never observed. Young and middle-aged adults with several tetanus pre-vaccinations accounted for the majority of side effects reported and in most cases hyperimmunization was suspected as a cause. As they were mainly restricted to the site of application and in 75% of cases occurred within 2-48 h, they can be interpreted as type III reactions (Arthus type). Furthermore it can be assumed that other causes of the reactions will have included unintentional intravascular and subcutaneous administration. Finally, one should also allow for the possibility of disease having coincided with the vaccination - especially in those cases where the reaction was not limited to the application site. More than 90% of all those adverse reactions occurring following a tetanus vaccination could thus be avoided by correct vaccination techniques and detailed vaccination anamnesis. [ABSTRACT FROM AUTHOR]

We investigated whether cardiac hypertrophy induced by volume loading influences baroreflex sensitivity. Aortic insufficiency (AI) was induced in male Wistar rats by graded disruption of the aortic valve, which, after 2 weeks, resulted in a 30% increase in heart/body weight or leftventricular/body weight ratio compared with control animals. Baroreflex sensitivity was assessed in conscious animals by measuring the heart rate (HR) responses to the changes in mean arterial pressure (MAP) induced by phenylephrine and nitroprusside sodium at 2 weeks. The slopes of the HR vs MAP plots obtained with phenylephrine and nitroprusside decreased significantly with increasing heart weight/body weight ratio (correlation coefficient r=0.625 and 0.526, respectively). In isolated right atria from AI animals baseline rate was higher, and the isoproterenol effect on sinus rate was significantly smaller than in atria from control animals, indicating a dysfunction of the β-adrenoceptor pathway. The data show that baroreflex dysfunction associated with a down-regulation of the β-adrenoceptor pathway of the sinus node develops simultaneously with volume overload-induced hypertrophy in the absence of overt heart failure. [ABSTRACT FROM AUTHOR]

In this study we have investigated the interaction of the loop diuretics torasemide and furosemide and of the eukalemic diuretic U-37883A (4-morpholinocarboximidine- N–1-adamantyl- N’-cyclohexylhydrochloride) with the ATP-sensitive K+ channel (KATP channel) in rat aortic rings. Torasemide contains a sulphonylurea group which might enable the compound to interfere with KATP channels; this group is lacking in furosemide. U-37883A blocks several types of KATP channels. The interaction with the vascular KATP channel was probed in binding studies, 86Rb+ efflux experiments and vasorelaxation assays. Torasemide inhibited the binding of the KATP channel inhibitor [3H]glibenclamide and of the opener [3H]P1075 with IC50 values of 19 and 45 µM, respectively; furosemide and U-37883A were inactive or interfered with binding in a nonspecific way. In 86Rb+ efflux experiments, the loop diuretics, at µM concentrations, inhibited basal tracer efflux to 50% whereas U-37883A had no effect. P1075-stimulated 86Rb+ efflux, a qualitative measure of KATP channel opening, was inhibited by U-37883A and torasemide with IC50 values of 0.06 and 130 µM, respectively; furosemide induced only a small (23%) inhibition. In experiments measuring isometric force, torasemide and furosemide partially relaxed endothelium-denuded aortic rings precontracted with noradrenaline or KCl with EC50 values between 6 and 10 µM. The vasorelaxant effect of P1075 was inhibited in a noncompetitive manner by torasemide (300 µM) but unaffected by furosemide. U-37883A increased noradrenaline-induced force and inhibited the vasorelaxant effect of P1075 in an apparently competitive manner with an inhibition constant of 0.4 µM. The data show that torasemide interferes specifically with the binding of the KATP channel modulators [3H]glibenclamide and [3H]P1075 and with the KATP channel opening and vasorelaxant effects of P1075 whereas furosemide is inactive. This suggests that the interaction of torasemide with the vascular KATP channel is due to the sulphonylurea group present in torasemide. U-37883A, which does not inhibit P1075 binding, is one of the most potent blockers of P1075-induced 86Rb+ efflux yet described but is relatively weak as an inhibitor of P1075-mediated vasorelaxation. The opposite vascular actions of torasemide and U-37883A are expected to contribute to the renal effects of these drugs. [ABSTRACT FROM AUTHOR]

In vascular smooth muscle, openers of ATP-dependent potassium channels (K ATP channels), such as P1075 ( N-cyano- N’-(1,1-dimethylpropyl)- N’’-3-pyridylguanidine), produce relaxation. In this study we have investigated the effects of thiol-modifying agents on the binding of P1075 and on the 86Rb+ efflux stimulating and vasorelaxant effects of the opener in rat aortic rings. The increase in 86Rb+ efflux induced by P1075 was taken as a qualitative measure of K+ channel opening. The hydrophilic SH-group-oxidizing substance, thimerosal (1 to 100μM), abolished specific binding of [3H]-P1075 with an IC50 value of 7.6±1.2μM; at 30μM, the half time for inhibition was 38min. Two other thiol-oxidizing agents, PMB (4-hydroxy-mercuribenzoic acid) and DTBNP (2,2’-dithio-bis(5-nitropyridine)), inhibited binding up to 86% and 44%, respectively. The disulphide bond reducing substance, DTT (1,4-dithiothreitol, 0.1 to 1mM), reduced [3H]-P1075 binding by up to 20% and partially reversed the inhibitory effect of thimerosal. In 86Rb+ efflux experiments, thimerosal (3 to 100μM) concentration-dependently increased basal efflux but inhibited P1075-stimulated tracer efflux with an IC50 value of 7±1μM. The inhibitory effect occurred with a half-time of approximately 8min and was essentially reversed by DTT. In rings precontracted with noradrenaline, thimerosal inhibited the vasorelaxant effect in a noncompetitive manner, shifting the concentration-relaxation curves to the right and reducing maximum relaxation.The data show that oxidation of thiol groups interferes with the binding of the K ATP channel opener, P1075; concomitantly, the 86Rb+ efflux stimulating and the vasorelaxant effects are inhibited. Reduction of disulphide bonds by DTT has only minor effects on the action of P1075. Collectively, the results suggest that intact thiol groups are essential for the functioning of the KATP channel in rat aorta. The different kinetics governing the inhibition of opener binding and of opener-stimulated 86Rb+ efflux suggest that the SH-groups involved in the two processes differ in their accessibility to thimerosal and/or in their reactivity. [ABSTRACT FROM AUTHOR]

In rat aortic rings, P1075, an opener of ATP-dependent potassium channels (KATP channels), produces relaxation and 86Rb+ efflux from preloaded tissues; the increase in 86Rb+ efflux qualitatively reflects KATP channel opening. In this study we have investigated the effects of protein kinase C modulation on the 86Rb+ efflux stimulating, the vasorelaxant and the binding properties of P1075. Phorbol 12,13-dibutyrate (PDBu), a direct activator of protein kinase C, inhibited the 86Rb+ efflux produced by P1075 with an IC50 value of 20±2nM. Phorbol 12-myristate 13-acetate (PMA), another stimulator of protein kinase C, was 150 times weaker in this respect whereas 4α-PDBu, the inactive stereoisomer of PDBu, was ineffective. Staurosporine (300nM), an inhibitor of protein kinase C, induced a small but significant increase of P1075-induced tracer efflux and partially reversed the inhibitory effect of PDBu on P1075-stimulated tracer efflux. The vasorelaxant effect of P1075 was inhibited only to a moderate degree by PDBu at concentrations which inhibited P1075-induced 86Rb+ efflux to >90%; however, in the presence of PDBu, the relaxation kinetics of P1075 were increasingly slowed. The vasorelaxant effect of P1075 in the presence of PDBu was still sensitive to inhibition by glibenclamide (100nM), the standard inhibitor of the KATP channel openers. Specific binding of [3H]-P1075 to rat aortic rings was unaffected by PDBu and PMA even in the micromolar concentration range. The data show that stimulation of protein kinase C inhibits the K+ channel opening effect of P1075 in rat aorta and suggest that protein kinase C may exert a weak tonic inhibition on the KATP channels in this vessel under quasiphysiological conditions. At concentrations of PDBu which essentially abolished P1075-induced tracer efflux, the glibenclamide-sensitive vasorelaxant effect of P1075 was slowed down but not prevented; this supports earlier suggestions that K+ channel openers are also able to relax smooth muscle cells by a mechanism independent of KATP channel opening. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is associated with major vascular complications. It was the aim of this study to examine the function of the ATP-sensitive K+ channel (KATP channel) in aortic rings prepared from diabetic rats and from age-matched controls. Diabetes was induced by injection of streptozotocin (60mg/kg i.p.) and the animals were sacrificed 10 weeks after treatment. The binding of the KATP channel opener, P1075 (N-cyano-N’-(1,1-dimethylpropyl)-N’’-3-pyridylguanidine), as well as the vasorelaxant and 86Rb+ efflux stimulating effects of the drug were measured. channel opener P1075 against noradrenaline was shifted rightwards by a factor of 1.3 and the maximum relaxation was reduced from 81 to 71% of initial tension ( P<0.01). However, specific binding of 3H-P1075 was increased by 20% without a change in affinity, indicating that the number of binding sites for the opener was increased as a consequence of diabetes. In addition, P1075-induced 86Rb+ efflux, a qualitative measure of KATP channel opening, was augmented by 50%. channel opening response to P1075 is markedly increased; however, the vasorelaxant effect to the KATP channel opener is slightly impaired. A possible explanation of these findings is that the vasorelaxant mechanisms (which are in part independent of plasmalemmal KATP channel opening) may be altered; alternatively, the link between membrane potential and smooth muscle tone may be changed in this model of insulin-dependent diabetes mellitus. [ABSTRACT FROM AUTHOR]

The effect of activators of protein kinase A on membrane K+ permeability and the interaction of these compounds with cromakalim, an opener of ATP-sensitive K+ channels (KATP channels), were investigated. Membrane K+ permeability was assessed by measuring 86Rb+ efflux from rings of rat aorta. Forskolin, an activator of adenylate cyclase, and isobutylmethylxanthine (IBMX), a nonselective phosphodiesterase inhibitor, induced small, concentration-dependent increases in tracer efflux up to 20-40% over the basal level. The effect of forskolin was abolished by the K+ channel blocker tedisamil (1 µM) and partially inhibited by glibenclamide (1 µM), a relatively selective blocker of KATP channels. Further studies were conducted in the presence of 35mM KCl in the bath in order to increase the size of the 86Rb+ efflux stimulated by forskolin and IBMX. At high concentrations, these compounds produced a biphasic effect with a peak increase being followed by a lower plateau value. Glibenclamide inhibited the 86Rb+ efflux response to forskolin and IBMX by 50-80%. The K+ channel blockers tedisamil (1 µM), Ba2+ (1mM) and tetraethylammonium (10mM) also reduced the peak response to forskolin by about 50% and abolished or greatly inhibited the plateau response. In addition to the small effect on basal 86Rb+ efflux, forskolin (0.3 µM) increased cromakalim-induced 86Rb+ efflux 3.4 times. At higher concentrations, however, a concentration-dependent inhibition was observed with an IC50 value of 7.6 ±0.4 µM. 1,9-dideoxyforskolin, which does not increase cAMP, increased neither basal nor cromakalim-induced 86Rb+ efflux; however, it inhibited cromakalim-stimulated tracer efflux with an IC50 value of 22 ±2 µM. It is concluded that forskolin and IBMX, probably by increasing intracellular cAMP levels, induce a 86Rb+ efflux from rat aorta, the major part of which is glibenclamide-sensitive and may pass through KATP channels. In addition, low concentrations of forskolin greatly facilitate the KATP channel opening effect of cromakalim whereas high concentrations block the channel; this blocking effect of forskolin is unrelated to the cAMP elevating action. [ABSTRACT FROM AUTHOR]

The kidney is endowed with ATP-sensitive K+ channels (KATP channels) both at the vascular and at the epithelial level. In this study we have characterized the binding of the sulphonylurea glibenclamide, the most widely used blocker of KATP channels, in rat isolated glomeruli. In metabolically intact glomeruli, 3H-glibenclamide labelled two different binding components with affinities of 47 ± 12 nM and 10 ± 1 μM and estimated binding capacities of 1.2 ± 0.1 and 501 ± 11 pmol/mg protein, respectively. 3H-glibenclamide binding was inhibited differentially by other sulphonylureas (tolbutamide, glibornuride, gliquidone and glipizide) and benzoic acid analogues such as meglitinide, AZ-DF 265 and UL-DF 9. Sulphonylureas interacted with the high affinity component and, in some cases, also with the low affinity component whereas the benzoic acid derivatives inhibited exclusively low affinity glibenclamide binding. Severe metabolic stress affected both components of glibenclamide binding by shifting high affinity binding to the right and reducing the capacity of the low affinity component. Disruption of the cytoskeletal actin filaments by cytochalasin B and D mimicked the effect of metabolic stress on the high affinity component but left the low affinity component unchanged. In crude membranes, the affinity of the first component was again reduced and a major loss of the low affinity sites was observed. The data show that the two binding components of glibenclamide binding in rat isolated glomeruli have very different properties. The high affinity component is not recognized by the benzoic acid derivatives; its affinity is modulated by cell metabolism and the actin component of the cytoskeleton. The low affinity sites are, in their majority, cytosolic. The function and cellular localization of the high affinity sites are under further study. [ABSTRACT FROM AUTHOR]

Copyright of Herz is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The interaction between the cytoskeleton and the ATP-sensitive K+ channel (KATP channel) was studied in rat aortic rings by examining the binding of the sulphonylurea blocker, 3H-glibenclamide, and of the opener, 3H-P1075. The actin cytoskeleton disrupting agents, cytochalasin D (1μM) and latrunculin B (1μM), abolished the high affinity component of 3H-glibenclamide binding. Preincubation with the actin cytoskeleton stabilizing agent, phalloidin (10μM) prevented the effect of cytochalasin D. In contrast, binding of the opener, 3H-P1075, and inhibition of this binding by glibenclamide, were unaffected by cytochalasin D (3μM). Colchicine (100μM), which disassembles microtubules, had no effect on the binding of 3H-glibenclamide and 3H-P1075. The data show that high affinity binding of glibenclamide, which mediates the effects of the sulphonylurea in this preparation, requires the presence of an intact actin cytoskeleton. Binding of the opener is unaffected by the state of the cytoskeleton and preserves a conformational state in which high affinity binding of glibenclamide to the sulphonylurea receptor can occur. [ABSTRACT FROM AUTHOR]