The whole cell patch clamp technique was used to study the effects of changes in [Ca2+](i) on the excitability of cultured dorsal root ganglion (DRG) neurones. Increases in [Ca2+](i) caused membrane depolarization, altered the characteristics of evoked action potentials and activated potassium, chloride and non-selective cation conductances. Mobilization of Ca2+ from intracellular stores with caffeine (1 mM) or ryanodine (10 μM) or photorelease of Ca2+ from DM-nitrophen gave rise to depolarizations suggesting a dominant inward current under our recording conditions of low [Ca2+](i) buffering capacity. The actions of [Ca2+](i) could be partially reversed by intracellular flash photolysis of diazo-2 but not by diazo-3. The electrophysiological properties of some DRG neurones were not influenced by changes in [Ca2+](i) and we suggest that this is because in this heterogeneous culture some neurones do not express Ca2+-activated ion channels. Copyright (C) 1999 Elsevier Science Ireland Ltd.
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