Streptomycin and intracellular calcium modulate the response of single guinea-pig ventricular myocytes to axial stretch

We tested the hypothesis that both stretch-activated channels (SACs) and intracellular calcium ([Ca2+](i)) are important in the electrical response of single guinea-pig ventricular myocytes to axial stretch. Myocytes were attached to carbon fibre transducers and stretched, sarcomere length increased by approximately 9 %, and there was a prolongation of the action potential duration. Streptomycin, a blocker of SACs, had no effect upon the shortening, [Ca2+](i) transients or action potentials of electrically stimulated, unstretched myocytes, at a concentration of 50 mum, but at 40 mum, prevented any stretch-induced increase in action potential duration. Under action potential clamp, stretch elicited a current with a linear current-voltage relationship that was inward at membrane potentials negative to its reversal potential of -30 mV, in 10 of 24 cells tested, and was consistent with the activation of non-specific, cationic SACs. This current was not seen in any stretched cells that were exposed to 40 mum streptomycin. However, exposure of cells to 5 mum BAPTA-AM, in order to reduce [Ca2+](i) transients, also abolished stretch-induced prolongation of the action potential. We conclude that both SACs and [Ca2+](i) are important in the electrical response of cardiac myocytes to stretch, and propose that stretch-induced changes in electrical activity and [Ca2+](i) maybe linked by inter-dependent mechanisms.