Pharmacological properties of the T-type Ca2+ current of mouse spermatogenic cells

Abstract

The effects of pharmacological agents on the T-type Ca2+ current were studied in dissociated spermatogenic cells from the mouse. Ca2+ currents were elicited by depolarization in 10 mM Ca2+ and recorded in the whole-cell configuration of the patch clamp technique. The T-type current was inhibited by the following compounds: PN200-110 (IC50 = 4 x 10(-8) M) > nifedipine (IC50 = 4 x 10(-7) M) > pimozide (IC50 = 4.6 x 10(-7) M) > mibefradil (IC50 = 5 x 10(-6) M) > Ni2+ (IC50 = 3.4 x 10(-5) M) > verapamil (IC50 = 7 x 10(-5) M) > amiloride (IC50 = 2.4 x 10(-4) M) > Cd2+ (IC50 = 2.8 x 10(-4) M). However, the agents differed in the reversibility and the use dependence of their effects. Currents recovered rapidly and completely after removal of Ni2+, Cd2+, amiloride, or mibefradil, whereas recovery from verapamil block was rapid but incomplete. In contrast, we observed little recovery after the removal of pimozide and of the dihydropyridines (PN200-110, nifedipine). Moreover, mibefradil and pimozide exhibit a strongly use-dependent inhibition of current that is due to selective interaction of these drugs with the open state and the inactivated state of the channel, respectively, rather than with the resting state. These properties of the spermatogenic T-type Ca2+ channel differ from those of somatic cell T channels and suggest a molecular diversity of low voltage-activated Ca2+ channels.