Double-pulse calcium channel current facilitation in adult rat sympathetic neurones

J Physiol. 1991 Aug;439:181-214. doi: 10.1113/jphysiol.1991.sp018663.

Abstract

1. Double-pulse facilitation of Ca2+ channel currents in enzymatically dispersed adult rat superior cervical ganglion neurones was investigated using the whole-cell variant of the patch-clamp technique. Voltage-clamp recordings were performed at room temperature (21-24 degrees C) in solutions designed to isolate Ca2+ channel currents. 2. Ba2+ currents, elicited by a 0 mV test pulse, were increased in amplitude when preceded by a 40 ms pulse to voltages greater than 0 mV. The magnitude of facilitation was dependent on pre-pulse voltage and reached a maximum of 50% (i.e. 1.5 x the current amplitude elicited without a pre-pulse) at a pre-pulse voltage of +80 mV. Half-maximal facilitation occurred at about +25 mV. A small decrease (-6%) in test pulse amplitude was present at pre-pulse voltages between -40 and 0 mV. The magnitude of facilitation was also dependent on test pulse voltage. Facilitation was greatest between test pulse voltages of -10 and 0 mV. 3. Facilitation slowly decreased during prolonged (1 h) dialysis of the neurone even though the Ba2+ current amplitude was well maintained. 4. Increasing the pre-pulse duration over the range 0-120 ms produced an exponential increase in facilitation with a time constant of 17.3 ms. Conversely, lengthening the interpulse duration over the range 5-915 ms, while maintaining a constant pre-pulse amplitude and duration, resulted in an exponential decrease in facilitation with a time constant of 197 ms. 5. At a test potential of 0 mV, the decay of the facilitated Ba2+ current component was fitted to a double exponential function with time constants of about 25 and 150 ms. The time constants had little pre-pulse voltage dependence between +30 to +80 mV. 6. The initial rising phase of both the control and facilitated Ba2+ current were reasonably well described by a single exponential (tau rise) after a delay of 300 microseconds. The tau rise versus test pulse potential relationship was 'bell shaped' over the test pulse voltage of -20 to +30 mV reaching a maximum near -5 mV. tau rise was similar for control and facilitated currents except at potentials greater than +10 mV where the rise of the facilitated current was accelerated. 7. Control and facilitated activation curves, as derived from tail current amplitudes, were described by the sum of two Boltzmann functions. A facilitating pre-pulse produced an increase in the proportion of the current contributed by the component activated at more hyperpolarized test potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

Publication types

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

MeSH terms

  • Animals
  • Barium / pharmacology
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / physiology*
  • GTP-Binding Proteins / pharmacology
  • Ganglia, Sympathetic / physiology*
  • Guanosine 5'-O-(3-Thiotriphosphate) / pharmacology
  • Male
  • Membrane Potentials
  • Mollusk Venoms / pharmacology
  • Neural Conduction
  • Nicotinic Acids / pharmacology
  • Oxadiazoles*
  • Rats
  • Rats, Inbred Strains
  • Virulence Factors, Bordetella / pharmacology

Substances

  • Calcium Channel Blockers
  • Calcium Channels
  • Mollusk Venoms
  • Nicotinic Acids
  • Oxadiazoles
  • Virulence Factors, Bordetella
  • PN 202-791
  • Barium
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • GTP-Binding Proteins