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Overexpression of calcineurin in transgenic mouse heart results in massive cardiac hypertrophy followed by sudden death. Sudden deaths are caused by abrupt transitions from sinus rhythm to heart block (asystole) in calcineurin-overexpressing (CN) mice. Preliminary studies showed decreased maximum change in potential over time (dV/[dt.sub.max]) of phase 0 of the action potential. Accordingly, the hypothesis was tested that decreased activity of the sodium channel contributes to heart block. Profound decreases in activity of sodium currents ([I.sub.Na]) paralleled the changes in action potential characteristics. Progressive age-dependent decreases were observed such that at 42-50 days of life little sodium channel function existed. However, this was not paralleled by decreased protein expression as assessed by immunocytochemistry or by Western blot. Since calcineurin can interact with the ryanodine receptor, we assessed whether chronic in vitro treatment with BAPTA-AM, thapsigargin, and ryanodine could rescue the decrease of [I.sub.Na]. All of these treatments rescued [I.sub.Na] to levels indistinguishable from wild type. The nonspecific PKC inhibitor bisindolylmaleimide I also rescued the decrease of [I.sub.Na]. TO assess whether decreased sodium channel activity contributes to sudden death in vivo, the response to encainide (20 mg/kg) was assessed: 6 of 10 young CN mice died because of asystole, whereas 0 of 10 wild-type mice died (P < 0.01). Moreover, encainide produced exaggerated prolongation of the QRS width in sinus beats before the heart block. Catecholamine tone appears necessary to support life in older CN mice because propranolol (1 mg/kg) triggered asystolic death in five of six CN mice. We conclude that decrease in sodium channel activity is in the common final pathway to asystole in CN mice. sodium current; transgenic mice; ryanodine receptor

Experiments were performed to investigate the properties of adenosine-triphosphate-dependent potassium channels (ATP-dependent K+) in myocytes from diabetic rat hearts. The action potentials of diabetic ventricular myocytes were recorded and analyzed. The findings suggest a strong influence of potassium ATP channels on the action potential configuration in the diabetic heart. This implies the resistance of the diabetic heart to the effects of ischemia.

The inhibition of L-type Ca2+ current induced through CCh and NO is mediated by cGMP in the mammalian heart. This in turn suggests that the pacemaker sinoatrial node cells, in the presence of ISO, are affected by the above mentioned biochemical pathway. Research on rabbit hearts is discussed, with emphasis on the relation between heart rate and Nitric Oxide.

A study of the effects of size and rate on the steady state (Iss) and transient (Ito) outward potassium currents in ventricular myocytes isolated from hypo-, hyper- and euthyroid rats using the whole cell, suction electrode voltage clamp technique reveals that thyroid status influences potassium currents in rat ventricle. A lower metabolic rate accompanies the reduction in Ito size under hypothyroid conditions. Excess thyroid hormone does not exert any general, nonspecific modulation of potassium channels.

A study of the alpha-adrenergic modulation of transient outward potassium current during hyperthyroidism is presented. Previous studies have shown that alpha-adrenoceptors are abundant in cardiac muscles and thus mediate positive inotropic effects. The study protocol involved measurements of K+ currents in single cardiac myocytes isolated from normal and from hyperthyroid rabbits. The results suggest that hyperthyroidism reduces the modulation of K+ currents, possibly by reducing the number and/or the affinity of alpha-adrenergic receptors.

A sustained [K.sup.+] current ([I.sub.ss]) is attenuated in ventricular cells from streptozotocin (STZ)-induced diabetic rats. The in vitro addition of insulin to isolated cells augments [I.sub.ss] in a process that is blocked by disrupting either actin microfilaments (with cytochalasin D) or microtubules (with colchicine). When these agents are added at progressively later times, the effect of insulin becomes evident in a time-dependent manner. [I.sub.ss] is also augmented by insulin in control cells in a cytoskeleton-dependent manner. However, in contrast to diabetic cells, cytoskeleton-dependent augmentation of [I.sub.ss] by insulin occurs at a considerably faster rate in control cells. Immunofluorescent labeling shows a reduced density of [Beta]-tubulin in diabetic cells, particularly in perinuclear regions. In vitro insulin replacement or in vivo insulin injections given to STZ-treated rats enhances [Beta]-tubulin density. These results suggest an impairment of cytoskeleton function and structure under insulin-deficient conditions, which may have implications for cardiac function. cardiac potassium channels; microtubules; actin microfilaments

Shimoni, Y., D. Severson, and H. S. Ewart. Insulin resistance and the modulation of rat cardiac [K.sup.+] currents. Am J Physiol Heart Circ Physiol 279: H639-H649, 2000.-- [K.sup.+] currents were measured using a whole cell voltage-clamp method in enzymatically isolated rat ventricular myocytes obtained from two hyperinsulinemic, insulin-resistant models. Fructose-fed rats as well as genetically obese rats, both of which are resistant to the metabolic effects of insulin, were used. The normal augmentation of a calcium-independent sustained [K.sup.+] current was reduced or abolished in insulin-resistant states. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadyl sulfate (3-4 wk treatment or after 5-6 h in vitro) enhanced the sustained [K.sup.+] current. The in vitro effect of vanadyl was blocked by cycloheximide. Insulin resistance of the [K.sup.+] current was not reversed by vanadyl sulfate. The results show that insulin resistance is expressed in terms of insulin actions on ion channels, in addition to its actions on metabolism. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadate compounds, which mimic the effects of insulin on metabolism, also mimic the augmenting effects of insulin on a cardiac [K.sup.+] current in a manner suggesting synthesis of new channels. cardiac potassium channels; diabetes mellitus; vanadate; metformin

Overexpression of calcineurin in transgenic mouse heart results in massive cardiac hypertrophy followed by sudden death. Sudden deaths are caused by abrupt transitions from sinus rhythm to heart block (asystole) in calcineurin-overexpressing (CN) mice. Preliminary studies showed decreased maximum change in potential over time (dV/dtmax) of phase 0 of the action potential. Accordingly, the hypothesis was tested that decreased activity of the sodium channel contributes to heart block. Profound decreases in activity of sodium currents (INa) paralleled the changes in action potential characteristics. Progressive age-dependent decreases were observed such that at 42-50 days of life little sodium channel function existed. However, this was not paralleled by decreased protein expression as assessed by immunocytochemistry or by Western blot. Since calcineurin can interact with the ryanodine receptor, we assessed whether chronic in vitro treatment with BAPTA-AM, thapsigargin, and ryanodine could rescue the decrease of INa. All of these treatments rescued INa to levels indistinguishable from wild type. The nonspecific PKC inhibitor bisindolylmaleimide I also rescued the decrease of INa. To assess whether decreased sodium channel activity contributes to sudden death in vivo, the response to encainide (20 mg/kg) was assessed: 6 of 10 young CN mice died because of asystole, whereas 0 of 10 wild-type mice died (P < 0.01). Moreover, encainide produced exaggerated prolongation of the QRS width in sinus beats before the heart block. Catecholamine tone appears necessary to support life in older CN mice because propranolol (1 mg/kg) triggered asystolic death in five of six CN mice. We conclude that decrease in sodium channel activity is in the common final pathway to asystole in CN mice. [ABSTRACT FROM AUTHOR]

Background Organ fragments can be cultured for weeks in vitro if they are prepared of microscopic thickness and if the basic organ structure is preserved. Such organ fragments, which we termed micro-organs (MOs), express in culture endogenous tissue-specific gene products. We have exploited this methodology to engineer MOs ex vivo by gene transfer. Methods MOs prepared from spleen, lung, colon and skin were infected using: herpes simplex type-1, adeno virus, vaccinia virus and murine leukemia virus (MuLV), carrying the reporter gene β-galactosidase. Results All four viral vectors infected MOs in culture, with adeno infection giving significantly higher values. After optimization, high levels of expression (>15% positive cells), comparable to those obtained with the adeno construct, were also obtained using the MuLV construct both in vitro and after implantation into syngeneic hosts. After implantation, the engineered tissue was found to remain localized, become vascularized, and to express the transduced gene for several months. Conclusions The system can be used to study interactions between viruses and tissues both ex vivo and in vivo. Furthermore, the approach proposes a novel platform for ex vivo gene therapy. Such engineered structures could be used as autologous biological pumps for continuous secretion in vivo of gene products of clinical importance. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Presents information on a study which tested the hypothesis that cytoskeleton-dependent effects of insulin on potassium currents follow a different time course in cardiac myocytes from control and diabetic rats. Methodology; Results and discussion.

Reports that in insulin resistance there is an attenuation or abolition of the augmenting effect of insulin on the steady-state K[sup +] current I[sub ss]. Separation of currents; Fructose-fed model; Reversal of insulin resistance by insulin-sensitizing drugs; Modulation of insulin sensitivity.

A ouabain like compound obtained from toad skin and plasma and identified to be a steroidal bufodienolide glycoside was found to displace ouabain from its binding site and to inhibit Na+-K+ATPase, and have positive inotropic effects on cardiac muscle. The ionic and rate dependence of this positive inotropy was studied in the frog atrium. The effect was dependent on extracellular potassium, sodium, and calcium concentrations and on the rate of stimulation, which is similar to the properties of cardiac glycosides. Occasionally, the compound gave transient or even negative inotropic responses, as do the glycosides. The action potential configuration was also affected by the compound in the same complex pattern as is that of cardiac glycosides.It is concluded that the endogenous bufodienolide compound has the same physiological effects as cardiac glycosides. Since the same compound is present in toad plasma it may serve as an intrinsic humoral regulator of cardiac contractility. This study is the first detailed characterisation of the cardioactive properties of this compound. [ABSTRACT FROM PUBLISHER]

Describes tests of inductive action of soluble factors on isolated chick epiblasts. Conditioned medium induced the formation of complex structures that constitute the embryonic axis, whereas various growth factors did not. Results show soluble factors behave as true morphogens.