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

Abstract

Using the patch-clamp technique in whole-cell configuration we have investigated the effect of increasing the internal calcium concentration (Ca_i) from below 10⁻⁸ M to 10⁻⁶ M on the three calcium currents: I_{Ca, T} (T for transient), I_{Ca, S} (S for sustained), I_{Ca, N} (N for neither), recently described in rat sensory neurones> Increasing Ca_i led to a dose-dependent reduction of the amplitude of I_{Ca, S} and, as Ca_i reached 5×10⁻⁷M I_{Ca, S} was nearly abolished. I_{Ca, 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 Ca_i dependent-inactivation, the increase of Ca_i from 5×10⁻¹⁰ M to 10⁻⁷ M. With Ca=5×10⁻⁷ M, all the cells displayed I_{Ca, T} and half of the cells in addition I_{Ca, N}, but it was of small amplitude. At Ca_i=10⁻⁶ M, most of the recorded cells only exhibited I_{Ca, T}.