Changes in single L-type calcium channel currents in CA1 pyramidal neurons of rat hippocampus after transient forebrain ischemia

It has been shown that intracellular Ca2+ in hippocampal CA1 neurons is elevated during ischemia and at early period following reperfusion. This Ca2+, overload has been suggested to be involved in ischemic brain damage. In normal CA1 neurons, the major mechanism allowing Ca2+ entry from the extracellular compartment is the opening of voltage-gated Ca2+ channels. The aim of the present study was to explore whether L-type calcium channel in hippocampal CA1 neurons changed at early period of reperfusion after ischemia. Transient forebrain ischemia in a duration of 15 min was induced by the use of the 4-vessel occlusion method in rats. Single L-type calcium currents were recorded in cell-attached patches of actually dissociated hippocampal CA1 neurons. After ischemia, average total patch current of L-type Ca2+ channels significantly increased in CA1 neurons when compared with that of control. This ischemia-induced enhancement in channel function was due to a higher channel open probability. Further analysis of single channel kinetics showed a prolonged open time and an increased opening frequency in postischemic channels. It is suggested that the functional enhancement in L-type calcium channels may partially account for the postischemic increase in intracellular Ca2+ concentration of CA1 neurons following ischemia.