Dual action of cytosolic calcium on calcium channel activity during hypoxia in hippocampal neurones.

The role of cytoplasmic calcium level (Ca(i)) in regulation of Ca channel activity during hypoxia was studied in hippocampal neurones from rats. Whole-cell patch clamp recordings in combination with measurements of O(2) partial pressure (pO(2)) were used. Lowering of pO(2) induced a potentiation of HVA Ca channel activity by 25.7% at Ca(i) = 75 nM in comparison with Ca(2+)-free solution. Increase of Ca(i) up to 410 nM slightly increased the effect and significantly slowed the Ca(2+) current run-down. On the other hand, hypoxia increased a steady-state channel inactivation and speeded up the kinetics of Ca(2+) current decay by about 30%. We conclude that moderate hypoxia induces dual action on Ca channels: intracellularly mediated augmentation of Ca influx via Ca channels and their Ca(2+)-dependent inactivation.