Voltage-dependent calcium channels in ventricular cells of rainbow trout: effect of temperature changes in vitro

Voltage-dependent calcium channels (VDCC) in ventricular myocytes from rainbow trout (Oncorhynchus mykiss) were investigated in vitro using the perforated patch-clamp technique, which maintains the integrity of the intracellular milieu. First, we characterized the current using barium as the charge carrier and established the doses of various pharmacological agents to use these agents in additional studies. Second, we examined the current at several physiological temperatures to determine temperature dependency. The calcium currents at 10 degrees C (acclimation temperature) were identified as L-type calcium currents based on their kinetic behavior and response to various calcium channel agonists and antagonists. Myocytes were chilled (4 degrees C) and warmed (18 and 22 degrees C), and the response of VDCC to varying temperatures was observed. There was no significant dependency of the current amplitude and kinetics on temperature. Amplitude decreased 25-36% at 4 degrees C (Q(10) approximately 1.89) and increased 18% at 18 degrees C (Q(10) approximately 1.23) in control, Bay K8644 (Bay K)-, and forskolin-enhanced currents. The inactivation rates (tau(i)) did not demonstrate a temperature sensitivity for the VDCC (Q(10) 1.23-1. 92); Bay K treatment, however, increased temperature sensitivity of tau(i) between 10 and 18 degrees C (Q(10) 3.98). The low Q(10) values for VDCC are consistent with a minimal temperature sensitivity of trout myocytes between 4 and 22 degrees C. This low-temperature dependency may provide an important role for sarcolemmal calcium channels in adaptation to varying environmental temperatures in trout.