Calcium permeability and modulation of nicotinic acetylcholine receptor-channels in rat parasympathetic neurons

J Physiol Paris. 1992;86(1-3):67-76. doi: 10.1016/s0928-4257(05)80009-9.


Neuronal nicotinic acetylcholine (ACh)-activated currents in rat parasympathetic ganglion cells were examined using whole-cell and single-channel patch clamp recording techniques. The whole-cell current-voltage (I-V) relationship exhibited strong inward rectification and a reversal (zero current) potential of -3.9 mV in nearly symmetrical Na+ solutions (external 140 mM Na+/internal 160 mM Na+). Isosmotic replacement of extracellular Na+ with either Ca2+ or Mg2+ yielded the permeability (Px/PNa) sequence Mg2+ (1.1) > Na+ (1.0) > Ca2+ (0.65). Whole-cell ACh-induced current amplitude decreased as [Ca2+]0 was raised from 2.5 mM to 20 mM, and remained constant at higher [Ca2+]0. Unitary ACh-activated currents recorded in excised outside-out patches had conductances ranging from 15-35 pS with at least three distinct conductance levels (33 pS, 26 pS, 19 pS) observed in most patches. The neuronal nicotinic ACh receptor-channel had a slope conductance of 30 pS in Na+ external solution, which decreased to 20 pS in isotonic Ca2+ and was unchanged by isosmotic replacement of Na+ with Mg2+. ACh-activated single channel currents had an apparent mean open time (tau 0) of 1.15 +/- 0.16 ms and a mean burst length (tau b) of 6.83 +/- 1.76 ms at -60 mV in Na+ external solution. Ca(2+)-free external solutions, or raising [Ca2+]0 to 50-100 mM decreased both the tau 0 and tau b of the nAChR channel. Varying [Ca2+]0 produced a marked decrease in NP0, while substitution of Mg2+ for Na+ increased NP0. These data suggest that activation of the neuronal nAChR channel permits a substantial Ca2+ influx which may modulate Ca(2+)-dependent ion channels and second messenger pathways to affect neuronal excitability in parasympathetic ganglia.

Publication types

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

MeSH terms

  • Acetylcholine / pharmacology
  • Amino Acid Sequence
  • Animals
  • Calcium / metabolism*
  • Calcium / physiology
  • Cations, Divalent / pharmacokinetics
  • Electric Conductivity
  • Ion Channels / genetics
  • Ion Channels / metabolism*
  • Molecular Sequence Data
  • Neurons / drug effects
  • Neurons / metabolism*
  • Neurons / physiology
  • Nicotine / metabolism*
  • Parasympathetic Nervous System / cytology
  • Parasympathetic Nervous System / metabolism*
  • Parasympathetic Nervous System / physiology
  • Permeability
  • Rats
  • Receptors, Nicotinic / metabolism*
  • Receptors, Nicotinic / physiology


  • Cations, Divalent
  • Ion Channels
  • Receptors, Nicotinic
  • Nicotine
  • Acetylcholine
  • Calcium