Ca2+ influx in resting rat sensory neurones that regulates and is regulated by ryanodine-sensitive Ca2+ stores

J Physiol. 1999 Aug 15;519 Pt 1(Pt 1):115-30. doi: 10.1111/j.1469-7793.1999.0115o.x.

Abstract

1. Store-operated, voltage-independent Ca2+ channels are activated by depletion of intracellular Ca2+ stores and mediate Ca2+ influx into non-excitable cells at resting membrane potential. We used microfluorimetry, patch-clamp and Mn2+-quench techniques to explore the possibility that a similar mechanism exists in rat dorsal root ganglion (DRG) neurones in primary culture. 2. Following caffeine-induced depletion, ryanodine-sensitive Ca2+ stores refilled with Ca2+ at resting membrane potential. The refilling process required extracellular Ca2+, was blocked by 2 mM Ni2+, and was facilitated by membrane hyperpolarization from -55 to -80 mV, indicating a key role for Ca2+ influx. This influx of Ca2+ was not affected by the voltage-operated Ca2+ channel (VOCC) antagonists nicardipine (10 microM), nimodipine (10 microM) or omega-grammotoxin SIA (1 microM). 3. When ryanodine-sensitive Ca2+ stores were depleted in Ca2+-free media, a return to 2 mM external Ca2+ resulted in a pronounced [Ca2+]i overshoot, indicating an increased permeability to Ca2+. Depletion of Ca2+ stores also produced a 2-fold increase in the rate of Mn2+ influx. The [Ca2+]i overshoot and Mn2+ entry were both inhibited by Ni2+, but not by VOCC antagonists. 4. Caffeine induced periodic Ca2+ release from, and reuptake into, ryanodine-sensitive stores. The [Ca2+]i oscillations were arrested by removal of extracellular Ca2+ or by addition of Ni2+, but they were not affected by VOCC antagonists. Hyperpolarization increased the frequency of this rhythmic activity. 5. These data suggest the presence of a Ca2+ entry pathway in mammalian sensory neurones that is distinct from VOCCs and is regulated by ryanodine-sensitive Ca2+ stores. This pathway participates in refilling intracellular Ca2+ stores and maintaining [Ca2+]i oscillations and thus controls the balance between intra- and extracellular Ca2+ reservoirs in resting DRG neurones.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Animals
  • Animals, Newborn
  • Biological Transport
  • Caffeine / pharmacology*
  • Calcium / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Cells, Cultured
  • Ganglia, Spinal / cytology
  • Ganglia, Spinal / physiology*
  • Membrane Potentials
  • Neurons, Afferent / cytology
  • Neurons, Afferent / physiology*
  • Nicardipine / pharmacology
  • Nimodipine / pharmacology
  • Patch-Clamp Techniques
  • Peptides, Cyclic / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Ryanodine / pharmacology*
  • Ryanodine Receptor Calcium Release Channel / physiology*

Substances

  • Calcium Channel Blockers
  • Peptides, Cyclic
  • Ryanodine Receptor Calcium Release Channel
  • omega-grammotoxin SIA
  • Ryanodine
  • Caffeine
  • Nimodipine
  • Nicardipine
  • Calcium