fainted in Great Britain © The Company of Biologists Limited 1987 STRETCH ACTIVATION OF A K + CHANNEL IN

Heart ventricle cells of Lymnaea stagnalis contain a stretch-activated K+ channel which exhibits two open states and three closed states. Over the range 0 to —25mmHg (1 mmHg = 133-3 Pa), the probability that the channel is open is a steeply non-linear function of negative pressure. Pressure-dependent decreases in the mean times of the longest component of the closed-time distribution are observed in the same range and (because other mean times show no consistent or sufficiently large changes with pressure) are assumed to account for increases in the probability of being open. Channel activity characteristically occurs as bursts with a mean time of 3-6ms. These bursts contain, on average, 1-7 closings; 78 % of the burst time is spent in the open state. It is concluded that the stretch-sensitive kinetic component is an interburst closed state