Enhancement of the Cav3.1 Channel Activity by PKA in Ventricular Myocytes of a1G Transgenic Mice

Abstract

Low voltage-activated T-type Ca2+ channels (Cav3 or TTCC) play an important role in regulating the pacemaker activities in the heart. Since adrenergic system is critical for heart rate regulation and the TTCC is involved in cardiac rhythmn generation, it is important to examine the regulation of the TTCC by the adrenergic-PKA system. In this study, we sought to resolve the question whether Cav3.1 in cardiac myocytes is regulated by PKA. Methods: Cav3.1 α1G transgenic mice were established with the cardiac specific and inducible system engineered by the Robbins group. Whole cell voltage clamp was used to measure the ICa-T before and after isoproterenol application. ICa-T was also recorded with or without cAMP (10μM) in the pipet. Results: (1) There is robust ICa-T (25.3±12.5pA/pF, n=13) in ventricular myocytes isolated from α1G TG mice but no ICa-T was observed in ventricular myocytes from control mice; (2) ICa-T in α1G TG myocytes was significantly increased by isoproterenol application (before vs. after: 15.0±3.3pA/pF, n=4 vs. 11.7±4.7pA/pF, n=4, at -40mV, p<0.05). This indicates Cav3.1 channel activity was probably up-regulated by isoproterenol-activated PKA in myocytes isolated from adult α1G transgenic mice. (3) cAMP can greatly increase both T-type (with vs. without cAMP: 48.9±29.2pA/pF, n=4 vs. 25.3±12.5pA/pF, n=13, maximal ICa-T, p<0.05) and L- type calcium currents (with vs. without cAMP: 19.9±7.4pA/pF, n=4 vs. 7.6±3.7pA/pF, n=13, maximal ICa-L, p<0.05). This further confirms the up-regulation effect of PKA on the Cav3.1 channel activity. Conclusions: For the first time, we found that PKA activation enhances Cav3.1 channel activity in ventricular myocytes of mice. This finding may shed a light on the physiological and pathophysiological (arrhythmogenic) effects of sympathetic regulation of pacemaker activities in the heart through T-type calcium channels.