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 cardi ac 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 wh ole cell patch clamp configuration. Isolated guinea-pig ventricular myocyte s 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 inactiva ted, its threshold was at negative potentials and was blocked by 40 mum Ni2 +. Disruption of microfilaments by cytochalasin D and of microtubules by co lchicine prevented the activation of I-CaT during cell swelling. Taxol had no effect. These results indicate that I-CaT is increased during cell swell ing and this effect needs an intact cyloskeleton. (C) 2001 Academic Press.