[Coupling of electrical processes on the membrane to the contractile activity of anococcygeus smooth muscle cells].

Rabbit anococcygeus smooth muscle cells (SMC) were studied by means of the double saccharose bridge method. The contractile apparatus of anococcygeus SMC was shown to be activated by two ways: by action potentials (AP) and by steady depolarization of the membrane potential. In view of the fact that calcium current blockers (Mn2+ and Cd2+) inhibit APs and phasic contractions, APs of SMC have calcium nature and phasic contractions are evoked by the same ions that are involved in AP generation and enter muscle cells via fast potential-dependent calcium channels. Since Cd2+ completely but reversibly blocks tonic contractions, it is assumed that the tonic component of contraction is also activated by extracellular calcium ions that enter muscle cells via so-called slow potential-dependent calcium channels activated by steady depolarization of muscle cells. Therefore, both phasic and tonic contractions in anococcygeus muscle cells are evoked largely by extracellular calcium ions.