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

We have previously reported the electrophysiological properties of sarcolemmal stretch-activated BKCa (SAKCA) channels cloned from cultured chick embryonic ventricular myocytes. However, the role of BKCa channels in the electrophysiology of the more mature heart is not clear. We have investigated the effects on the BKCa 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 BKCa 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 BKCa current from post-hatch ventricular myocytes. The present results suggest that axial stretch activates BKCa channels via a stretch-induced increase in the cytosolic Na+ concentration followed by an increased Ca2+ influx.