A novel Ca(2+) influx pathway in mammalian primary sensory neurons is activated by caffeine

J Neurophysiol. 2001 Jul;86(1):190-6. doi: 10.1152/jn.2001.86.1.190.

Abstract

Single-cell microfluorimetry and electrophysiology techniques were used to identify and characterize a novel Ca(2+) influx pathway in adult rabbit vagal sensory neurons. Acutely dissociated nodose ganglion neurons (NGNs) exhibit robust Ca(2+)-induced Ca(2+) release (CICR) that can be triggered by 10 mM caffeine, the classic agonist of CICR. A caffeine-induced increase in cytosolic-free Ca(2+) concentration ([Ca(2+)](i)) is considered diagnostic evidence of the existence of CICR. However, when CICR was disabled through depletion of intracellular Ca(2+) stores or pharmacological blockade of intracellular Ca(2+) release channels (ryanodine receptors), caffeine still elicited a significant rise in [Ca(2+)](i) in approximately 50% of NGNs. The same response was not elicited by pharmacological agents that elevate cyclic nucleotide concentrations. Moreover, extracellular Ca(2+) was obligatory for such caffeine-induced [Ca(2+)](i) rises in this population of NGNs, suggesting that Ca(2+) influx is responsible for this rise. Simultaneous microfluorimetry with whole cell patch-clamp studies showed that caffeine activates an inward current that temporally parallels the rise in [Ca(2+)](i). The inward current had a reversal potential of +8.1 +/- 6.1 (SE) mV (n = 4), a mean peak amplitude of -126 +/- 24 pA (n = 4) at E(m) = -50 mV, and a slope conductance of 1.43 +/- 0.79 nS (n = 4). Estimated EC(50) values for caffeine-induced CICR and for caffeine-activated current were 1.5 and approximately 0.6 mM, respectively. These results indicate that caffeine-induced rises in [Ca(2+)](i), in the presence of extracellular Ca(2+), can no longer be interpreted as unequivocal diagnostic evidence for CICR in neurons. These results also indicate that sensory neurons possess a novel Ca(2+) influx pathway.

Publication types

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

MeSH terms

  • Animals
  • Caffeine / pharmacology*
  • Calcium / pharmacokinetics*
  • Calcium-Transporting ATPases / antagonists & inhibitors
  • Calcium-Transporting ATPases / metabolism
  • Central Nervous System Stimulants / pharmacology*
  • Dose-Response Relationship, Drug
  • Electrophysiology
  • Enzyme Inhibitors / pharmacology
  • Female
  • Hydroquinones / pharmacology
  • Male
  • Mammals
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Neurons, Afferent / drug effects
  • Neurons, Afferent / metabolism*
  • Rabbits
  • Ryanodine / pharmacology

Substances

  • Central Nervous System Stimulants
  • Enzyme Inhibitors
  • Hydroquinones
  • Ryanodine
  • 2,5-di-tert-butylhydroquinone
  • Caffeine
  • Calcium-Transporting ATPases
  • Calcium