Inhibition of voltage-dependent Ca2+ channels of porcine tracheal smooth muscle by the novel Ca2+ channel antagonist RWJ-22108

We compared electrophysiological effects of the bronchoselective Ca2+ channel antagonist RWJ-22108 on voltage-dependent Ca2+ channels (VDCs) of porcine tracheal smooth muscle cells to the effects of nicardipine and verapamil. 2. Each of the three Ca2+ channel antagonists tested inhibited inward Ca2+ currents (ICa) measured by whole-cell patch clamp techniques. Inhibition was dose-dependent with approximately 50% inhibition of peak ICa at +20 mV obtained with 3 x 10(-6) M RWJ-22108, 3 x 10(-7) M nicardipine, or 10(-5) M verapamil. 3. Both RWJ-22108 (3 x 10(-6) M) and nicardipine (3 x 10(-7) M) shifted the voltage dependence of steady-state inactivation to more negative potentials; however, the change in the potential of half-maximal inactivation induced by RWJ-22108 (-18 mV) was significantly greater than that induced by nicardipine (-12 mV). Verapamil did not alter the voltage dependence of inactivation. 4. We conclude that inhibition of VDCs by RWJ-22108 is qualitatively similar to that by nicardipine but with a greater stabilizing effect on the inactivated channel state.