Two Types of Ca Channels in Smooth Muscle Cells Isolated from Guinea-Pig Taenia Coli

Abstract

Ca influx through Ca channels in smooth muscle cells plays a crucial role in both membrane excitation and muscle contraction. In 1985, we demonstrated that a single Ca channel currents, with Ba ions acting as charge carriers, could be recorded by the cell attached patch clamp method in enzymatically isolated smooth muscle cells of guinea pig taenia coli (Yoshino and Yabu, 1985). Recent patch clamp studies has provided evidence that multiple types of Ca channels exist in many excitable cells. It has been suggested that each channel type contributes to different physiological functions, such as a source of Ca ions during excitation-contraction coupling, the generation of pacemaker activity and the release of transmitter from nerve terminals. Two different types of Ca channels has also been reported for smooth muscle cell membrane, mainly vascular muscles, from single channel recordings(Aaronson et al., 1986; Benham et al., 1987) and whole cell recording (Sturek and Hermsmeyer, 1986; Bean et al., 1986). We examined whether different types of Ca channels in mamalian intestinal smooth muscles cells from guinea-pig taenia coli (Yoshino et al., 1987; Yoshino et al., 1988). Then, we concluded that both channel types represent fast and slow inactivating voltage dependent Ca channels exist in this cell.