Enhancement of the T-type calcium current by hyposmotic shock in isolated guinea-pig ventricular myocytes

It is known that swelling and shrinkage of cardiac cells can modulate their electrical activity. However, the effects of osmotic manipulation on cardiac T type calcium current (I-CaT) has not been previously reported. In this study, the have examined the effects of cell swelling on ka,, using the whole cell patch clamp configuration. Isolated guinea-pig ventricular myocytes were swollen by an external hypotonic challenge (0.7 T). We found that I-CaT is enhanced during a hypotonic shock. This current has been determined to be the T type calcium current since it is rapidly activated and inactivated, its threshold was at negative potentials and was blocked by 40 mum Ni2+. Disruption of microfilaments by cytochalasin D and of microtubules by colchicine prevented the activation of I-CaT during cell swelling. Taxol had no effect. These results indicate that I-CaT is increased during cell swelling and this effect needs an intact cyloskeleton. (C) 2001 Academic Press.