A COMPARATIVE STUDY OF ANAESTHETIC AGENTS ON HIGH VOLTAGE ACTIVATED CALCIUM CHANNEL CURRENTS IN IDENTIFIED MOLLUSCAN NEURONS

Using the two electrode voltage clamp configuration, a high voltage activated whole-cell Ca2+ channel current (IBa) was recorded from a cluster of neurosecretory Light Yellow Cells (LYC) in the right parietal ganglion of the pond snail Lymnaea stagnalis. Recordings of IBa from LYCs show a reversible concentration-dependent depression of current amplitude in the presence of the volatile anaesthetics halothane, isoflurane and sevoflurane, or the non-volatile anaesthetic pentobarbitone at clinical concentrations. In the presence of the anaesthetics investigated, IBa measured at the end of the depolarizing test pulse showed proportionally greater depression than that at measured peak amplitude, as well as significant decrease in the rate of activation or increase in inactivation or both. Within the range of concentrations used, the concentration-response plots for all the anaesthetics investigated correlate strongly to straight line functions, with linear regression R2 values > 0.99 in all instances. For volatile anaesthetics, the dose-response regression slopes for IBa increase in magnitude, in order of gradient: sevoflurane, isoflurane and halothane, a sequence which reflects their order of clinical potency in terms of MAC value.