Electrophysiological properties of L-type Ca2+ currents in isolated adult mouse ventricular myocytes

The whole-cell configuration of the patch-clamp technique was used to analyze the electrophysiological characteristics of the L-type calcium current (ICa) in single ventricular myocytes from hearts of adult mice. In Tyrode solution, ICa activated ar -30mV peaked at 0 mV, and reverted near +60 mV, the peak current density was -8.1 +/- 2.5 pA/pF (N = 14). In a Na(+)- and K(+)-free solution containing 12 microM tetrodotoxin, and 10 mM Ca2+ or Ba2+ as charge carrier, the current-voltage relationship and the voltage dependence of inactivation were shifted about 10 mV to more depolarized voltages. The maximum Ba2+ current was two-times greater than the maximum Ca2+ current. The voltage dependencies of steady-state activation and inactivation were determined within the range of -70 to ł mV and fitted with Boltzmann relations. The Ca2+ current showed half-maximal activation at -9.94 +/- 3.86 mV (slope factor (k) = 5.9 +/- 0.68 mV) and half-maximal inactivation at -27.65 +/- 5.74 mV (k = 6.37 +/- 2.79 mV), while the Ba2+ current showed half-maximal activation at -0.35 +/- 2.43 mV (k = 6.0 +/- 0.84 mV) and half-maximal inactivation at -20.33 +/- 2.40 mV (k = 5.36 +/- 1.10 mV). The time course of recovery of Ba2+ current from inactivation could be described using a single exponential function with a time constant of 83.37 msec. The overlap of activation and inactivation curves suggests the existence of an L-type Ca2+ window current with a maximal amplitude near -20mV.