In vivo and in vitro inhibition of the L-type calcium current in isolated guinea pig cardiomyocytes by the immunosuppressive agent cyclosporin A

Cyclosporin A (CsA), an immunosuppressive agent used to reduce rejection after organ transplantation, induces secondary effects in heart tissue. We have studied the effects in vivo and in vitro of CsA on L-type Ca2+ current (I-Ca) and the associated gating currents of isolated guinea-pig ventricular myocytes using the whole-cell patch-clamp technique. For in vivo experiments, a group of animals (n = 28) was treated for 21 days by subcutaneous injection of CsA (15 mg/kg/day). Blood level of CsA was 1191 +/- 221 ng/ml (n = 9). In cells from these animals (n = 65, 19 animals), I-Ca was reduced to about 75% of that recorded from control cells (n = 32, six animals). CsA decreased the availability of Ca2+ channels at potentials more positive than + 30 mV. Isoproterenol (100 nM) was still able to increase I-Ca but only by 30 +/- 6% (n = 9), whereas in control it increased I-Ca by 290 +/- 22% (n = 5). Gating currents related to L-type Ca2+ channels were not altered in cells from CsA-treated animals. In in vitro experiments, CsA reduced I-Ca when applied directly to cardiomyocytes. CsA affected the kinetics of I-Ca inactivation, slowing down the rapid phase and accelerating the slow phase (n = 4). The steady state inactivation curve of I-Ca was shifted to more negative voltages and the degree of availability at -80 mV decreased by in vitro application of CsA. The half inactivation potential (V-1/2) changed from -23 +/- 0.6 mV in control to -31 +/- 2 mV, -48 +/- 0.6 mV and -49 +/- 0.6 mV, in 1, 50 and 80 mu M CsA, respectively. In these cells, the gating currents related to L-type Ca2+ channels were also not altered by CsA. CsA does not modify the Ca2+ channel density, although it induces a decrease in the beta(1)-adrenergic stimulation of I-Ca. The results are explained by a direct effect on the calcium channel inactivation of CsA and a non specific indirect effect. (C) 1997 Academic Press Limited.