Effect of internal calcium concentration on calcium currents in rat sensory neurones

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Abstract
Using the patch-clamp technique in whole-cell configuration we have investigated the effect of increasing the internal calcium concentration (Cai) from below 10−8 M to 10−6 M on the three calcium currents: ICa, T (T for transient), ICa, S (S for sustained), ICa, N (N for neither), recently described in rat sensory neurones> Increasing Cai led to a dose-dependent reduction of the amplitude of ICa, S and, as Cai reached 5×10−7M ICa, S was nearly abolished. ICa, N is well evidenced from 5×10−10 M to 10−7 M where its is a large current. Preliminary observations indicate an increase of its inactivation rate following, as expected for a possible Cai dependent-inactivation, the increase of Cai from 5×10−10 M to 10−7 M. With Ca=5×10−7 M, all the cells displayed ICa, T and half of the cells in addition ICa, N, but it was of small amplitude. At Cai=10−6 M, most of the recorded cells only exhibited ICa, T.