Stretch‐activated single ion channel currents in tissue‐cultured embryonic chick skeletal muscle.

Abstract

The membrane of tissue‐cultured chick pectoral muscle contains an ionic channel which is activated by membrane stretch. Nicotinic channels and Ca2+‐activated K+ channels are not affected by stretch. In 150 mM‐external K+ and 150 mM‐internal Na+ the channel has a conductance of 70 pS, linear current‐voltage relationship between ‐50 and ‐140 mV and a reversal potential of +30 mV. Kinetic analysis of single‐channel records indicates that there are one open (O) and three closed (C) states. The data can be fitted by the reaction scheme: C1‐C2‐C3‐O. Only the rate constant that governs the C1‐C2 transition (k1,2) is stretch‐sensitive. None of the rates are voltage‐sensitive. The rate constant k1,2 varies with the square of the tension as k1, 2 = k0 X e alpha T2, where alpha is a constant describing the sensitivity to stretch and T is the tension. A typical value of alpha is 0.08 (dyn cm‐1)‐2. Following exposure to cytochalasin B the channel becomes more sensitive to stretch. The stretch‐sensitivity constant, alpha, increases from 0.08 to 2.4 (dyn cm‐1)‐2. The probability of the channel being open is strongly dependent upon the extracellular K+ concentration. With a suction of 2 cmHg the probability increases from 0.004 in normal saline (5 mM‐K+) to 0.26 in 150 mM‐K+. The channel appears to gather force from a large area of membrane (greater than 3 X 10(5) A2), probably by a cytochalasin‐resistant cytoskeletal network.