Ryanodine receptor-mediated intracellular calcium release in rat cerebellar Purkinje neurones.
1. Ryanodine receptor-mediated Ca2+ release was investigated in Purkinje neurones of rat cerebellar slices by using whole-cell patch-clamp recordings combined with fluorometric digital imaging of cytoplasmic Ca2+ concentration ([Ca2+]i). 2. Caffeine caused a transient increase in [Ca2+]i in the somata and dendrites of Purkinje neurones. Caffeine-induced Ca2+ transients were not associated with a membrane inward current and persisted in Ca(2+)-free external solutions, indicating that they are caused by Ca2+ released from intracellular stores. The amplitudes of the caffeine-mediated elevations in [Ca2+]i were strongly dependent on the baseline level of [Ca2+]i. 3. Intracellular application of Ruthenium Red through the patch pipette blocked caffeine-induced Ca2+ transients in Purkinje neurones. Ryanodine when applied either intra- or extracellularly caused a use-dependent block of caffeine-induced Ca2+ release. 4. Depolarization-induced Ca2+ transients were strongly prolonged by caffeine. Several lines of evidence suggest that these prolongations reflect Ca(2+)-induced Ca2+ release. 5. Despite the presence of skeletal muscle type ryanodine receptors in Purkinje neurones, depolarizing pulses failed to induce any changes in [Ca2+]i when the influx of Ca2+ through voltage-gated channels was prevented by using Ca(2+)-free solution, or when applying blockers of voltage-gated Ca2+ channels. 6. Dendritic Ca2+ transients produced by stimulation of the excitatory climbing fibre synaptic input were also prolonged by caffeine, indicating that ryanodine receptor-mediated release of Ca2+ may be involved in synaptic signalling in cerebellar Purkinje neurones. 7. Ryanodine receptor-mediated release of Ca2+ in cerebellar Purkinje neurones can be explained by a model in which release of Ca2+ is strongly facilitated by the co-operative action of Ca2+, caffeine and/or ryanodine. Our results suggest that Ca2+ release in these central neurones becomes prominent only during episodes of intensive electrical activity associated with increased Ca2+ entry.
D000818:Animals; D002110:Caffeine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D004594:Electrophysiology; D005470:Fluorometry; D007425:Intracellular Membranes / Q000378:metabolism*; D009124:Muscle Proteins / Q000502:physiology*; D009412:Nerve Fibers / Q000502:physiology; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011689:Purkinje Cells / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel; D013569:Synapses / Q000502:physiology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009124:Muscle Proteins; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D012430:Ruthenium Red; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium