© 1999 by European Society of Cardiology
Copyright © 1999, European Society of Cardiology
Insulin stimulates the L-type Ca2+ current in rat cardiac myocytes
aMedical University Clinic, Institute of Clinical Biochemistry and Pathobiochemistry, 97080 Würzburg, Germany
bPhysiological Chemistry II, Theodor-Boveri-Institut für Biowissenschaften, 97074 Würzburg, Germany
* Corresponding author. Tel.: +49-931-201-2775; fax: +49-931-201-2775; e-mail: m.kirstein@medizin.uni-wuerzburg.de
Objective: The aim was to study the L-type calcium current (ICa,L) in cardiac myocytes as a possible target of insulin in the regulation of cardiac function. Method: Using the whole-cell configuration of the patch–clamp technique, we investigated the stimulation of ICa,L by insulin in isolated rat ventricular myocytes. Results: The stimulation of ICa,L by insulin was dose-dependent (EC50=33 nM) and reversible. Maximum stimulation of ICa,L over basal ICa,L was 86±11% (n=25) at 1 µM insulin. Insulin (1 µM) shifted the current–voltage relationship and potential-dependent availability of ICa,L to more negative potentials by about 3.5 and 1.5 mV, respectively. The maximum conductance of ICa,L was increased by 1 µM insulin, from 26±4 to 39±5 nS (n=11). Isoproterenol (100 nM), which stimulated ICa,L by 156±23% (n=10) over basal ICa,L, acted faster than insulin. The half-maximum stimulation of ICa,L by isoproterenol and insulin was reached after 44±5 and 80±9 s, respectively. Insulin and isoproterenol responses were not additive. Insulin (1 µM) and isoproterenol (100 nM) stimulation of ICa,L was inhibited by Rp-cAMPS (1 mM) to 12±3 and 32±4%, respectively. Insulin (1 µM) increased cAMP content in rat cardiomyocytes by about two-fold. Insulin-like growth factor-1 (IGF-1; 5 µM) increased ICa,L by only 5.9±0.9% (n=6). Conclusions: Our data show that insulin stimulates the L-type calcium current in isolated rat ventricular myocytes in a dose-dependent and reversible manner and suggest that this effect is mediated by insulin receptors and the cAMP-dependent protein kinase.
KEYWORDS Calcium current, L-type; Rat, ventricular myocytes; Patch–clamp; cAMP
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