Essential Role of Extracellular Ca²⁺ for the Maintenance of the Ca²⁺ Activated K⁺ Channel Activity in Guinea Pig Vas Deferens

Abstract

The characteristics of Ca²⁺ activated K⁺ channels of enzymatically dissociated single smooth muscle cells of vas deferens of the adult guinea pig were studied by the whole cell clamp technique. A stepwise depolarization to -30mV induced a fast transient current followed by the spontaneous transient outward currents (STOCs). STOCs were eliminated by application of K⁺ channel blocker TEA. STOCs appeared only when Ca²⁺ was present in extracellular medium, and disappeared immediately once Ca²⁺ was removed from the medium. Therefore, STOCs in the present preparation can be ascribed to the activity of Ca²⁺ activated K⁺ channels. Furthermore, even in the absence of Ca²⁺, STOCs were evoked transiently by application of caffeine, indicating the involvement of the Ca²⁺ induced Ca²⁺ release (CICR) mechanism. Thus, it is likely that Ca²⁺ activated K⁺ channels are operated via CICR mechanism and extracellular Ca²⁺ is essential for keeping their constant activity.