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 (ICaT) has not been previously reported. In this study, we have examined the effects of cell swelling on ICaT+ 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 ICaT 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 μM Ni2+. Disruption of microfilaments by cytochalasin D and of microtubules by colchicine prevented the activation of ICaT during cell swelling. Taxol had no effect. These results indicate that ICaT is increased during cell swelling and this effect needs an intact cytoskeleton. © 2001 Academic Press.