Calcium‐activated currents in cultured neurones from rat dorsal root ganglia

Voltage‐activated Ca²⁺ currents and caffeine (1 to 10 mm) were used to increase intracellular Ca²⁺ in rat cultured dorsal root ganglia (DRG) neurones. Elevation of intracellular Ca²⁺ resulted in activation of inward currents which were attenuated by increasing the Ca²⁺ buffering capacity of cells by raising the concentration of EGTA in the patch solution to 10 mm. Low and high voltage‐activated Ca²⁺ currents gave rise to Cl⁻ tail currents in cells loaded with CsCl patch solution. Outward Ca²⁺ channel currents activated at very depolarized potentials (V_c + 60 mV to + 100 mV) also activated Cl⁻ tail currents, which were enhanced when extracellular Ca²⁺ was elevated from 2 mm to 4 mm. The Ca²⁺‐activated Cl⁻ tail currents were identified by estimation of tail current reversal potential by use of a double pulse protocol and by sensitivity to the Cl⁻ channel blocker 5‐nitro 2‐(3‐phenylpropylamino) benzoic acid (NPPB) applied at a concentration of 10 μm. Cells loaded with Cs acetate patch solution and bathed in medium containing 4 mm Ca²⁺ also had prolonged Ca²⁺‐dependent tail currents, however these smaller tail currents were insensitive to NPPB. Release of Ca²⁺ from intracellular stores by caffeine gave rise to sustained inward currents in cells loaded with Cs acetate. Both Ca²⁺‐activated tail currents and caffeine‐induced inward currents recorded from cells loaded with Cs acetate were attenuated by Tris based recording media, and had reversal potentials positive to 0 mV suggesting activity of Ca²⁺‐activated cation channels. Our data may reflect (a) different degrees of association between Ca²⁺‐activated channels with voltage‐gated Ca²⁺ channels, (b) distinct relationships between channels and intracellular Ca²⁺ stores and Ca²⁺ homeostatic mechanisms, (c) regulation of Ca²⁺‐activated channels by second messengers, and (d) varying channel sensitivity to Ca²⁺, in the cell body of DRG neurones. 1992 British Pharmacological Society