E(f)-current contributes to whole-cell calcium current in low calcium in frog sympathetic neurons

J Neurophysiol. 2001 Sep;86(3):1156-63. doi: 10.1152/jn.2001.86.3.1156.

Abstract

Because Ca(2+) plays diverse roles in intracellular signaling in neurons, several types of calcium channels are employed to control Ca(2+) influx in these cells. Our experiments focus on resolving the paradox of why whole-cell current has not been observed under typical recording conditions for one type of calcium channel that is highly expressed in frog sympathetic neurons. These channels, referred to as E(f)-channels, are present in the membrane at a density greater than the channels that carry approximately 90% of whole-cell current in low Ba(2+); but, E(f)-current has not been detected in low Ba(2+). Using Ca(2+) instead of Ba(2+) as the charge carrier, we recorded a possible E-type current in frog sympathetic neurons. The current was resistant to specific blockers of N-, L-, and P/Q-type calcium channels but was more sensitive to Ni(2+) block than was N- or L-current. Current amplitude in Ca(2+) is slightly greater than that in Ba(2+). In 3 mM Ca(2+), the current contributed approximately 12% of total current at peak voltage and increased at voltages more hyperpolarized to the peak, reaching approximately 40% at -30 mV, where whole-cell current starts to activate. The presence of E(f)-current in 3 mM Ca(2+) suggests a potential role for E(f)-channels in regulating calcium influx into sympathetic neurons.

Publication types

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

MeSH terms

  • 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / pharmacology
  • Animals
  • Barium / pharmacology
  • Calcium / pharmacokinetics*
  • Calcium Channel Agonists / pharmacology
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels, L-Type / metabolism
  • Calcium Channels, N-Type / metabolism
  • Ganglia, Sympathetic / cytology
  • Ganglia, Sympathetic / physiology*
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Neurons / physiology*
  • Nickel / pharmacology
  • Nimodipine / pharmacology
  • Patch-Clamp Techniques
  • Rana catesbeiana
  • omega-Conotoxin GVIA / pharmacology
  • omega-Conotoxins / pharmacology

Substances

  • Calcium Channel Agonists
  • Calcium Channel Blockers
  • Calcium Channels, L-Type
  • Calcium Channels, N-Type
  • omega-Conotoxins
  • voltage-dependent calcium channel (P-Q type)
  • omega-conotoxin-MVIIC
  • Barium
  • Nimodipine
  • 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
  • Nickel
  • omega-Conotoxin GVIA
  • Calcium