Characterization of stretch‐activated nonselective cation channels in pregnant rat uterine smooth muscle

Abstract

Although the exact mechanisms that initiate parturition have been still uncertain, the stretching of the myometrium as a result of fetal growth has been considered as one of key event in the initiation of labor. However, the direct evidence for the presence of stretch‐activated non‐selective cation channels(SACC) in uterine smooth muscle has not yet been reported. In this study, the stretch can activate the SACC in pregnant rat myometrial cells using patch clamp technique. The application of negative pressure within a pipette in cell‐attached or inside‐out patch mode induced the opening of ion channels, which has single channel conductance of ~25pS, and activity of these ion channels are disappeared after removing of negative pressure. There was no significant difference in the stretch‐induced activation of ion channel between cell‐attached and inside‐out patch mode, which might exclude the possible involvement of secondary messenger systems in the activation of these channel by stretch. The channels shows similar permeability to both Na+ and Cs+ ions. Increasing [Ca2+]i in inside‐out patch mode significantly enhanced the channel activity at same negative pressure. From these result, it may be concluded that stretch can directly activate the SACC in pregnant rat uterine smooth muscle cells, and SACC might contribute to the spontaneous contraction during labor.