Effects of calcitonin gene-related peptide (CGRP) on Ca²⁺-channel current of isolated smooth muscle cells from rat vas deferens

Summary

Effects of calcitonin gene-related peptide (CGRP), a putative non-adrenergic non-cholinergic neutrotransmitter on the electrical properties of the cell membrane, were investigated in enzymically dispersed smooth muscle cells from rat vas deferens. Under current clamp conditions, CGRP (up to 10⁻⁷ M) did not induce significant changes in membrane potentials or input resistance in the resting state. The configurations of action potentials elicited by depolarizing current pulses were also unaffected, except that a prolongation of the duration of the action potentials by a high dose (10⁻⁷ M) of CGRP was observed in some of the cells. Under whole cell voltage clamp conditions, the transient and sustained K⁺ currents, activated by depolarizing voltage-steps, were apparently decreased in the presence of 10⁻⁹ to 10⁻⁷ M CGRP. The peptide increased the voltage-gated Ca²⁺ current in cells loaded with 145 mM Cs⁺ solution in order to block the K+ currents. The voltage-dependency of the peak Ca²⁺ current was not changed by CGRP. Ba²⁺ (10.8 mM) was used as a charge carrier for the Ca²⁺-channel current to clarify further the effects of CGRP on the properties of the current. CGRP (10⁻⁸ M) delayed the inactivation time course of the Ca²⁺-channel current and slowed the recovery from inactivation. The peptide did not affect the steady-state inactivation measured by changing the holding potential. The Ca²⁺-channel current in the presence of CGRP was suppressed by nicardipine (10⁻⁶ M) to the same extent as the current under control conditions. The results suggest that CGRP modifies the L-type Ca²⁺ channel in smooth muscle cells.