Single-channel properties of four calcium channel types in rat motoneurons.
Previous studies have demonstrated multiple components of whole-cell calcium currents in hypoglossal motoneurons (HMs); HMs possess a low-voltage-activated (LVA) current and three types of high-voltage-activated (HVA) calcium currents based on sensitivity to omega-Aga IVA, omega-Conotoxin GVIA (omega-CgTx) and dihydropyridine analogs (DHPs). In the present study, we recorded single-calcium channel activities from HMs using a cell-attached patch-clamp method and found four types of channels that could be discriminated based on kinetics, voltage dependency, DHP sensitivity, and single-channel conductances. The average single-channel conductances with 110 mM barium as a charge carrier were 7, 14, 20, and 28 pS. T-type channels had a single-channel conductance of 7 pS, activated at the most negative potentials for the calcium channels and inactivated during depolarization. L-type channels (DHP-sensitive channels) did not inactivate during depolarization and had a 28-pS single-channel conductance. Based on kinetics and sensitivity to holding potential, it is likely that the channels with conductances of 14 pS and 20 pS represent N-type and P-type channels, respectively. The N-type channel (14 pS) was sensitive to holding potential, showed modal gating, and inactivated during maintained depolarizations, whereas the P-type channel (20 pS) was rather insensitive to holding potential and did not inactivate during depolarization.
Umemiya
M
M
Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195.
Berger
A J
AJ
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology; D007002:Hypoglossal Nerve / Q000737:chemistry / Q000502:physiology; D009046:Motor Neurons / Q000737:chemistry / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000145:classification / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013111:Spider Venoms / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D015220:Calcium Channels; D004095:Dihydropyridines; D009419:Nerve Tissue Proteins; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D020866:omega-Conotoxin GVIA; D009543:Nifedipine