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

Abstract

The whole-cell recording technique was used to investigate the actions of a calcium release channel ligand, ryanodine, on calcium-activated chloride conductances, 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 calcium-induced calcium release in the cell bodies of cultured DRG neurones. Action potential after-depolarizations were attenuated by extracellular application of the chloride channel blocker, niflumic acid (10 microM), and by ryanodine (10 microM); these actions occurred without concurrent changes in evoked action potentials. Ryanodine and caffeine (10 mM) activated calcium-dependent conductances and the responses to ryanodine were attenuated by depletion of caffeine-sensitive Ca2+ stores. The current clamp data were complicated by changes in potassium conductances so studies were carried out under voltage clamp and voltage-activated calcium currents and calcium-activated chloride and non-selective cation currents were isolated pharmacologically. Ryanodine (10 microM) evoked delayed, inward, calcium-activated non-selective cation and chloride currents which reversed close to 0 mV and were attenuated by N-methyl-D-glucamine, niflumic acid and dantrolene. Consistent with actions on action potential after-depolarizations, niflumic acid (10 microM) and ryanodine (10 microM) attenuated calcium-activated chloride currents evoked by calcium entry through voltage-activated calcium channels. Niflumic acid and ryanodine had no effects on voltage-activated calcium currents evoked from a holding potential of -90 mV by voltage step commands to 0 mV. In conclusion calcium-activated chloride conductances appear to be activated in part by calcium released from ryanodine-sensitive stores, and significant calcium-induced calcium release may occur locally in cell bodies of DRG neurones as a result of calcium entry through voltage-activated channels during an action potential.

CaMKII inactivation by extracellular Ca2+ depletion in dorsal root ganglion neurons

“…DRG neurons express all of the components that underlie capacitative Ca 2+ -entry (CCE) and Ca 2+ -induced Ca 2+ release (CICR) commonly observed in non-excitable cells [11][12][13][14]. Both RyR-and IP 3 R-sensitive Ca 2+ stores have been demonstrated to be functionally coupled in DRG neurons and contribute to intracellular Ca 2+ signaling [15].…”

Intracellular mechanisms participating in the formation of neuronal calcium signals

“…It was also shown that calcium-activated chloride channels in these neurons are responsible for afterdepolarization following action potentials, and [I Cl ] Ca can be activated by calcium influx through voltage-activated calcium channels. According to Ayar and Scott [1], extracellular application of Ry to DRG neurons in a choline chloridebased extracellular solution and with a CsCl-based patch-pipette solution produced, transient inward currents at 0 mV. The pattern of Ry-induced inward currents varied from long-lasting sustained currents to more transient events.…”

“…[1]). However, it is of importance that not only such a global event plays a great role in the cell function.…”

Store-Dependent Entry of Ca2+ into Sensory Neurons of the Rat

“…Experiments dealing with the sensitivity of the basal intracellular Са 2+ concentration to the extracellular concentration of this ion show the actuality of such a way for Са 2+ entry into neurons [6]. The phenomenon of spontaneous replenishment of the ryanodine (Ry)-sensitive stores of the endoplasmic reticulum (ER) at a resting membrane potential in sympathetic [2] and sensory neurons [7], and also in hippocampal nerve cells [8], served as another proof of the existence of an alternative mechanism underlying the entry of Са 2 into the nerve cell. The main physiological role of the above store-dependent entry of Са 2+ into the nerve cells is the following: it allows the cell to rapidly replenish intracellular calcium stores, which is necessary for providing repetitive activation of the neuron [9].…”