title: Single calcium channel behavior in native skeletal muscle.
abstract: The purpose of this study was to use whole-cell and cell-attached patches of cultured skeletal muscle myotubes to study the macroscopic and unitary behavior of voltage-dependent calcium channels under similar conditions. With 110 mM BaCl2 as the charge carrier, two types of calcium channels with markedly different single-channel and macroscopic properties were found. One class was DHP-insensitive, had a single-channel conductance of approximately 9 pS, yielded ensembles that displayed an activation threshold near -40 mV, and activated and inactivated rapidly in a voltage-dependent manner (T current). The second class could only be well resolved in the presence of the DHP agonist Bay K 8644 (5 microM) and had a single-channel conductance of approximately 14 pS (L current). The 14-pS channel produced ensembles exhibiting a threshold of approximately -10 mV that activated slowly (tau act approximately 20 ms) and displayed little inactivation. Moreover, the DHP antagonist, (+)-PN 200-110 (10 microM), greatly increased the percentage of null sweeps seen with the 14-pS channel. The open probability versus voltage relationship of the 14-pS channel was fitted by a Boltzmann distribution with a VP0.5 = 6.2 mV and kp = 5.3 mV. L current recorded from whole-cell experiments in the presence of 110 mM BaCl2 + 5 microM Bay K 8644 displayed similar time- and voltage-dependent properties as ensembles of the 14-pS channel. Thus, these data are the first comparison under similar conditions of the single-channel and macroscopic properties of T current and L current in native skeletal muscle, and identify the 9- and 14-pS channels as the single-channel correlates of T current and L current, respectively.
authors.affiliation: Department of Physiology, Colorado State University, Fort Collins 80523, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: Dirksen
authors.forename: K G
authors.initials: KG
authors.lastname: Beam
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D017609:Barium Compounds / Q000493:pharmacokinetics; D002104:Cadmium / Q000494:pharmacology; D019256:Cadmium Chloride; D015220:Calcium Channels / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D002712:Chlorides / Q000493:pharmacokinetics / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D017275:Isradipine / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D009124:Muscle Proteins / Q000819:agonists / Q000037:antagonists & inhibitors; D018482:Muscle, Skeletal / Q000166:cytology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques
chemical_list: D017609:Barium Compounds; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002712:Chlorides; D004095:Dihydropyridines; D009124:Muscle Proteins; D002104:Cadmium; C028521:lanthanum chloride; C024986:barium chloride; D007811:Lanthanum; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D019256:Cadmium Chloride; D017275:Isradipine