Fig. 7. Currents through voltage-sensitive Ca²⁺ channels. (A) Typical currents through Ca²⁺ channels of Kenyon cells (left) and projection neurons (right) show different amplitudes of inward currents. Currents were elicited by depolarizing voltage pulses (-90 to +60 mV, increment 10 mV; duration 100 ms; holding potential -80 mV); protocol (inset). Tetraethylammonium chloride (TEA, 10 mmoll^-1) and 100 nmoll^-1 TTX were added to the external standard saline (ES std., see Materials and methods). To block K⁺ outward currents further, the internal saline contained CsF (40 mmoll^-1), Cs-gluconate (83 mmoll^-1), Cs-EGTA (10 mmoll^-1) and TEA-Cl instead of the corresponding K⁺ salts (cf. Materials and methods section). (B) Addition of 50 µmoll^-1 CdCl₂ (Cd²⁺) blocked the voltage-sensitive Ca²⁺ currents completely in Kenyon cells. A small residual Cd²⁺-insensitive current remained unblocked in projection neurons. The Cd²⁺ block was irreversible even after excessive periods of wash (up to 30 min). (C) Current—voltage relationships of the currents through voltage-sensitive Ca²⁺ currents of all measured neurons show different amplitudes of peak inward currents (measured at the time point indicated by the arrow in A) and diversity of Ca²⁺ currents between neurons of a given type. The amplitudes of the peak currents are higher in projection neurons (PN, right) than in those of Kenyon cells (KC, left). However, the voltage-dependencies of the currents and the variability of the current amplitudes at the various potentials (-90 to +60 mV) appear to be similar.

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