Unitary current analysis of L-type Ca2+ channels in human fetal ventricular myocytes

Abstract

Introduction: L-type calcium channels were studied in cell-attached patches from ventricular cell membranes of human fetal heart. Methods and Results: Experiments were performed in the presence of 70 mM Ba2+ as the charge carrier at 22°C to 24°C. Unitary current sweeps were evoked by 300- msec depolarizing pulses to 0 mV from a holding potential of -50 mV at 0.5 Hz. Recorded currents were blocked by nisoldipine (1 μM) and stimulated by (-)Bay K 8644 (1 μM). During control, channel activity was seen in 13.9% ± 4.2% of the total 200 sweeps. Ensemble average current amplitude was 0.03 ± 0.01 pA (n = 6) and average conductance was 20.4 ± 0.2 pS (n = 5). Analysis of single channel kinetics showed open time and closed time histograms were best fit by one and two exponentials, respectively. Mean open time was τ(o) = 0.99 ± 0.05 msec (n = 6). Mean closed time fast (τ(cf)) and slow (τ(cs)) component values were τ(cf) = 0.85 ± 0.09 msec and τ(cs) = 8.0 ± 0.94 msec (n = 6), respectively. With intrapipette (-)Bay K 8644 (1 μM), mean open time was best fit by two exponentials, τ(of) = 0.9 ± 0.2 msec (n = 10) and τ(os) = 13.4 ± 2.6 msec (n = 10); mean close time values were τ(cf) = 0.6 ± 0.1 msec (n = 10) and τ(cs) = 9.8 ± 1.9 msec (n = 10), respectively. With (-)Bay K 8644, channel activity was 66.5% ± 7.4%, the ensemble average current was 0.52 ± 0.04 pA (n = 10) and the conductance 20.7 ± 0.5 pS (n = 5). Conclusion: (1) the data establishes the characteristics of L-type Ca channels of human fetal hearts and their modulation by dihydropyridines; (2) the open time kinetics differ from those of avian embryonic and rat fetal hearts; and (3) the findings provide new and relevant information for understanding the physiologic behavior of unitary Ca2+ channels in the developing human heart and the baseline comparison for diseases that implicate Ca2+ channels in their etiology, such as autoimmune-associated congenital heart block.