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

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Abstract
1 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 (Vc + 60 mV to + 100 mV) also activated Cl− tail currents, which were enhanced when extracellular Ca2+ was elevated from 2 mm to 4 mm. 2 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. 3 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. 4 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.