An investigation of calcium-induced calcium-release (CICR) in cultured rat sensory neurones

Description

In this study the mechanisms of Ca²⁺-induced-Ca²⁺-release, effects of membrane depolarizations and the actions of pharmacological intracellular Ca²⁺-modulators were examined in cultured rat dorsal root ganglion (DRG) neurones. The whole cell configuration of the patch clamp technique was used to record action potentials, action potential after-potentials and voltage-activated calcium currents, (I_Ca), calcium-activated chloride currents, (I_CI(Ca)), and non-selective cation currents, (I_CAN), under current and voltage clamp recording conditions, respectively. A sub population of DRG neurones expressed action potential after-depolarizations and I_CI(Ca)tail currents which were due to activation of Ca²⁺-activated Cl^- channels as a result of Ca²⁺ entry. I_CANwas dominantly activated due to Ca²⁺ release from intracellular stores evoked by pharmacological Ca²⁺-releasing agents such as caffeine, ryanodine and dihydrosphingosine. Calcium-activated conductances were identified by estimating reversal potentials of the activated currents, using selective pharmacological blockers and extracellular ionic replacement studies. Calcium-dependence of activated currents was also examined by using high concentration of intracellular Ca²⁺ buffer, EGTA, to prevent elevation of intracellular Ca²⁺-levels and by rapidly buffering raised intracellular Ca²⁺ using intracellular 'caged Ca²⁺ chelator', diazo-2. The involvement of intracellular Ca²⁺- stores was examined by performing experiments in Ca²⁺-free extracellular recording medium and pharmacologically inhibiting release of Ca²⁺ from intracellular stores, using dantrolene. Ryanodine had complex actions on DRG neurones, which reflected its ability to mobilize Ca²⁺, deplete Ca²⁺ stores, and inhibit Ca²⁺ release channels. Ryanodine inhibited action potential after-depolarizations and I_CI(Ca)tail currents by interacting with intracellular stores and preventing amplification of Ca²⁺ signalling by CICR. It was found that CICR observed under physiological conditions in rat DRG neurones involves intracellular Ca²⁺stores which were sensitive to ryanodine. In addition to ryanodine sensitivity these intracellular Ca²⁺ stores could be mobilized by caffeine and dihydrosphingosine.

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572

Additional Fields

Identifer	oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:285521
Date	January 1997
Creators	Ayar, Ahmet
Publisher	University of Aberdeen
Source Sets	Ethos UK
Detected Language	English
Type	Electronic Thesis or Dissertation