EFFECTS OF MECHANICAL STRETCH ON MEMBRANE CURRENTS OF SINGLE VENTRICULAR MYOCYTES OF GUINEA-PIG HEART

A technique to record whole cell membrane current during stretching single cardiac myocytes was developed. Ventricular myocytes were dissociated by treating guinea-pig hearts with collagenase. One end of the cell was fixed either to a microglasstool tip or to a glass plate, while the other end was attached either to a microglasstool tip or to a suction pipette, which was mounted on a micromanipulator. A time-independent current showing a reversal potential of -15+/-4 mV (n = 7) was activated when the myocytes were stretched more than 20% of the length between two fixed point. The current gradually relaxed during the maintained stretch, and disappeared on releasing the stretch. We failed to detect any consistent change in either the L-type Ca2+ current or the inward rectifier K+ current. For comparison, current changes induced by inflating the cell using a hypo-osmotic solution were recorded. The inflation was not accompanied by any change in the time-independent current. Instead, the delayed rectifier K+ current was increased to 170+/-48% control by the 70% hypo-osmotic solution. Thus, the effect of mechanical stretch on the time-independent current is different from those of hypo-osmotic cell inflation. The stretch-induced time-independent current is compared with reported current changes induced by the intracellular microinjection of Ca2+.