Two types of calcium channels are expressed in adult bovine chromaffin cells.
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.
Bossu
J L
JL
Laboratoire d'Etude des Régulations Physiologiques, Centre National de la Recherche Scientifique, Strasbourg, France.
De Waard
M
M
Feltz
A
A
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D010456:Peptides, Cyclic / Q000494:pharmacology; D020960:omega-Conotoxins
D015220:Calcium Channels; D010456:Peptides, Cyclic; D020960:omega-Conotoxins; C053423:Conus magus toxin; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002118:Calcium