The actions of ryanodine on Ca2+-activated conductances in rat cultured DRG neurones; evidence for Ca2+-induced Ca2+ release

The whole-cell recording technique was used to investigate the actions of a calcium release channel ligand, ryanodine, on calcium-activated chloride c onductances, and to evaluate ryanodine-sensitive Ca2+-induced Ca2+ release from intracellular stores in cultured neonatal rat DRG neurones. The aim of the project was to use ryanodine as a pharmacological tool to evaluate cal cium-induced calcium release in the cell bodies of cultured DRG neurones. A ction potential after-depolarizations were attenuated by extracellular appl ication of the chloride channel blocker, niflumic acid (10 mu M), and by ry anodine (10 mu M); these actions occurred without concurrent changes in evo ked action potentials. Ryanodine and caffeine (10 mM) activated calcium-dependent conductances and the responses to ryanodine were attenuated by depletion of caffeine-sensit ive Ca2+ stores. The current clamp data were complicated by chang es in pot assium conductances so studies were carried out under voltage clamp and vol tage-activated calcium currents and calcium-activated chloride and non-sele ctive cation currents were isolated pharmacologically Ryanodine (10 mu M) e voked delayed, inward, calcium-activated non-selective cation and chloride currents which reversed close to 0 mV and were attenuated by N-methyl-D-glu camine, niflumic acid and dantrolene. Consistent with actions on action pot ential after-depolarizations, niflumic acid (10 mu M) and ryanodine (10 mu M) attenuated calcium-activated chloride currents evoked by calcium entry t hrough voltage-activated calcium channels. Niflumic acid and ryanodine had no effects on voltage-activated calcium currents evoked from a holding pote ntial of -90 mV by voltage step commands to 0 mV. In conclusion calcium-activated chloride conductances appear to be activate d in part by calcium released from ryanodine-sensitive stores, and signific ant calcium-induced calcium release may occur locally in cell bodies of DRG neurones as a result of calcium entry through voltage-activated channels d uring an action potential.