Abstract 14120: PKCd, but not PKCa, Regulates Spontaneous Firing of the Cardiac Pacemaker
Spontaneous beating of the heart is controlled by spontaneous firing of sinoatrial node cells (SANC) and is linked to rhythmic, submembrane local Ca2+ releases (LCR) from the sarcoplasmic reticulum (SR). LCR characteristics are regulated by high basal level of protein kinase A (PKA) and Ca2+ calmodulin-dependent protein kinase II (CaMKII) in SANC. Spontaneous, rhythmic LCRs activate inward Na+/Ca2+exchange current (INCX), imparting an exponential increase to the later part of the diastolic depolarization (DD) to fire an action potential (AP). Recently we have demonstrated that spontaneous firing of SANC, in addition to PKA and CaMKII, is critically dependent on protein kinase C (PKC), i.e. inhibition of PKC activity by either GF109203X (10 μmol/L) or calphostin C (1 μmol/L) markedly suppressed SR Ca2+ cycling and stopped spontaneous beating of freshly isolated rabbit SANC. The PKC superfamily includes approximately 12 different subtypes, and PKC-α has been identified as a critical regulator of Ca2+ handling and contractility in cardiac ventricular myocytes. To test hypothesis that PKC-α regulates spontaneous beating of SANC through modulation of Ca2+ cycling we employed specific PKC-α inhibitor Go-6976. Surprisingly Go-6976 (10 μmol/L) had no effects on either LCR characteristics (confocal microscopy, Ca2+ indicator Fluo-3) or spontaneous beating of freshly isolated rabbit SANC (perforated patch-clamp technique). However, inhibition of PKCδ activity by rottlerin (3 μmol/L) significantly decreased the LCR size (from 6.2±0.3 to 2.3±0.3 μm, n=3) and number per each spontaneous cycle (from 1.2±0.2 to 0.4±0.3, n=3). Rottlerin also markedly increased the LCR period (the time from the prior AP-induced Ca2+ transient to the appearance of LCR), which delineates the time of INCX activation and therefore regulates the spontaneous SANC beating rate. Consistent with this finding rottlerin markedly and time-dependently decreased DD rate leading to an increase in the spontaneous cycle length, and finally spontaneous SANC firing stopped. Thus, activity of PKCδ, but not PKCα, is critically important for spontaneous firing of cardiac pacemaker cells.
- © 2013 by American Heart Association, Inc.