Two types of calcium channels are expressed in adult bovine chromaffin cells

J Physiol. 1991 Jun;437:621-34. doi: 10.1113/jphysiol.1991.sp018615.

Abstract

1. Calcium channel activity was recorded in chromaffin cells in the cell-attached condition, using 110 mM-Ba2+ as the permeant ion. 2. One type of calcium channel had a conductance of 16 pS, was completely inactivated at a holding potential of -20 mV and was insensitive to dihydropyridine agonists and antagonists. These characteristics correspond to a calcium channel of the N-type. 3. A second type of calcium channel was active at holding potentials of -30 mV and above, had a channel conductance of 31 pS, and was sensitive to the dihydropyridine agonist, Bay K 8644. The channel opened along two dominant modes with characteristic time constants of 0.5 and 5 ms. The main effect of Bay K 8644 was to increase the probability of both short and long openings with no change in their relative proportions (6 to 1 respectively). These characteristics correspond to a calcium channel of the L-type. 4. omega-Conotoxin affected the activity of both N- and L-type channels. It drastically reduced the number of N-type channel openings and produced complex changes in L-type channel activity. Long openings were less frequent and the conductance during short openings was slightly smaller than that measured in the presence of Bay K 8644. 5. The discussion focuses on modulation of L-type channel activity. Openings of L-type channels are rarely recorded in the cell-attached configuration under control conditions. Addition of Bay K 8644 is needed to reveal the presence of L-type channels. By contrast, L-type currents recorded in the whole-cell configuration are always observed and are insensitive to Bay K 8644. These results indicate that L-type channels are normally inoperable in chromaffin cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / pharmacology
  • Animals
  • Calcium / metabolism
  • Calcium Channels / metabolism
  • Calcium Channels / physiology*
  • Cattle
  • Cells, Cultured
  • Chromaffin System / metabolism*
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Membrane Potentials / physiology
  • Peptides, Cyclic / pharmacology
  • omega-Conotoxins*

Substances

  • Calcium Channels
  • Peptides, Cyclic
  • omega-Conotoxins
  • Conus magus toxin
  • 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
  • Calcium