Effects on L-type calcium current of agents interfering with the cytoskeleton of isolated guinea-pig ventricular myocytes

We studied the effects of an external acute 10 min application of cytoskeletal interfering agents on cardiac L-type calcium current (I-Ca,I-L). We found that colchicine, taxol and cytochalasin D had no direct effect on the L-type calcium channel as indicated by the absence of effect on voltage-dependent parameters. Phalloidin induced a shift in the I-V curve which renders it difficult to use in excitation-contraction coupling studies. Microfilaments of actin did not seem to regulate cardiac I-Ca,I-L as indicated by the lack of effect of cytochalasin D on I-Ca,I-L amplitude and inactivation kinetics. On the contrary, microtubules seem to be involved in the calcium-dependent inactivation of I-Ca,I-L. This involvement might be direct, i.e. a physical link between the microtubules and some part of the channel protein, or it could be indirect, i.e. the calcium chelating properties and physical obstacle of microtubules in the space between the sarcolemma and the SR.