Electrophysiological properties of L-type Ca2+ currents in isolated adult mouse ventricular myocytes
Nascimento, J.H.
Brazilian Journal of Medical and Biological Research 29(10): 1397-1405
1996
ISSN/ISBN: 0100-879X PMID: 9181116 Document Number: 466579
The whole-cell configuration of the patch-clamp technique was used to analyze the electrophysiological characteristics of the L-type calcium current (I-Ca) in single ventricular myocytes from hearts of adult mice. In Tyrode solution, I-Ca activated at -30 mV peaked at 0 mV, and reverted near +60 mV. At 0 mV, the peak current density was -8.1 +- 2.5 pA/pF (N = 14). In a Na+- and K+-free solution containing 12 mu-M tetrodotoxin, and 10 mM Ca-2+ or Ba-2+ as charge carrier, the current-voltage relationship and the voltage dependence of inactivation were shifted about 10 mV to more depolarized voltages. The maximum Ba-2+ current was two-times greater than the maximum Ca-2+ current. The voltage dependencies of steady-state activation and inactivation were determined within the range of -70 to +50 mV and fitted with Boltzmann relations. The Ca-2+ 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 Ba-2+ 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 Ba-2+ 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 Ca-2+ window current with a maximal amplitude near -20 mV.