Calcium Signaling in Myocytes of Injured Myocardium

Abstract

Calcium signaling during cardiac excitation-contraction coupling is compromised after myocardial injury (MI). Myocytes of injured myocardium display reduced synchronization of calcium spikes at low calcium current density indicating worsened communication between sarcolemmal DHPR and sarcoplasmic reticulum RyR calcium channels [1]. Here we study the activation of Ca-spikes by using strong synchronized calcium triggers. Cardiac myocytes were isolated from left ventricles of young adult male Wistar rats on day 15 after administration of a single high dose of isoproterenol, to model the myocardial injury (MI), or a vehicle as the control, and studied by means of the whole cell patch clamp and confocal microscopy techniques. Ca-spikes were activated by a short prepulse to +60 mV from a holding potential of −50 mV and subsequent step repolarization to negative voltages that induced perfectly synchronized influx of Ca2+ ions via DHPR channels. Ca-spikes were recorded using 100 μM fluo-3 and 1 mM EGTA at 2 kHz line scan frequency. In this arrangement, increase of the calcium influx increased the probability of Ca-spike activation in the same manner in both the control and MI groups. The probability of local Ca2+ release was not different between the two groups. In the MI group, the amplitude of Ca-spikes was increased and the latency of spikes was abbreviated relative to controls. Both effects could be explained by increased sarcoplasmic reticulum Ca2+ load revealed by caffeine application. We conclude that the DHPR-RYR calcium coupling in MI myocytes functions well when the triggering calcium influx is strong, most likely due to sensitizing effect of increased sarcoplasmic reticulum Ca2+ load on RyR activation by calcium.Supported by grants APVV-0721-10 and VEGA 2/0197/11.