Effects of axial stretch on sarcolemmal BK_Ca channels in post-hatch chick ventricular myocytes

We have previously reported the electrophysiological properties of sarcolemmal stretch-activated BK_Ca (SAKCA) channels cloned from cultured chick embryonic ventricular myocytes. However, the role of BK _Ca channels in the electrophysiology of the more mature heart is not clear. We have investigated the effects on the BK_Ca current of axial stretch in post-hatch ventricular myocytes. Whole-cell currents of ventricular myocytes isolated from 2-week-old chicks were recorded using the patch-clamp technique, while the cells were either held at resting length or stretched to cause a 10% increase in sarcomere length using a pair of carbon fibres attached to opposite ends of the cell. Stretch did not affect whole-cell currents immediately after the stretch was applied. However, sustained stretch for 3 min significantly increased outward currents. This stretch-induced change was reversed by applying 10 nm iberiotoxin, a specific BK_Ca channel blocker, or a Na⁺-Ca²⁺-free environment. These results were reproduced in a computer simulation study. The present study is the first report about the sarcolemmal BK_Ca current from post-hatch ventricular myocytes. The present results suggest that axial stretch activates BK _Ca channels via a stretch-induced increase in the cytosolic Na ⁺ concentration followed by an increased Ca²⁺ influx.