The kinetic characteristics of the L-type calcium channels in cardiocytes of hibernators. 1. Development of a kinetic model.

The present paper described the experimental and theoretical investigations of the kinetic characteristics of the L-type Ca2+ channels in ground squirrels Citellus undulatus in two different physiological states (hibernation and spontaneous arousal). The perforated patch-clamp method was used in the experiments. It is shown that the potential-dependent Ca2+ current in isolated cardiocytes from hibernating animals is strongly inhibited during hibernation. An attempt was made to describe the kinetics of Ca2+ currents by the modified Hodgkin-Huxley equations. The experimental current traces are compared to the nonstationary solutions of the modified model, and the model parameters were found by optimization methods. It is shown that the simple dmfn model, where d is activation, f is inactivation, can not be used to describe the experimental characteristics at any power values m and n. Analysis of other models based on the conception of independence of activation and inactivation processes showed that in both physiological states-hibernation and spontaneous arousal-Ca2+ current was described by the model d2f1(2)f2, where d is activation, f1 and f2 are slow (f1-type) and fast (f2-type) inactivations of the channel.