title: Dihydropyridine-sensitive calcium channels expressed in canine colonic smooth muscle cells.
abstract: Experiments were performed to identify and characterize the types of calcium channels that regulate inward calcium current in canine colonic smooth muscle. Freshly dispersed smooth muscle cells from the circular layer of the canine proximal colon were used. Single-channel currents were measured with 80 mM Ba2+ as the charge carrier. Small-conductance (10 +/- 2 pS, EBa = 46 +/- 11 mV, n = 9) and large-conductance (21 +/- 1 pS, EBa = 52 +/- 3 mV, n = 19) single-channel currents were observed during depolarizing voltage steps positive to -30 mV. Both types of single-channel currents were inhibited by the addition of 10(-6) M nifedipine to the bath solution. The smaller current was infrequently observed and therefore was not further characterized. Open probability (P(o)) of the larger current amplitude was strongly dependent on voltage. Activation curves were well described by a Boltzmann function with half activation occurring at 4 mV, and a 5-mV increase in membrane potential resulted in an e-fold increase in P(o). BAY K 8644 (1 microM) shifted the activation curve to the left while nifedipine (1 microM) resulted in a right shift. Molecular analysis showed that only the C class of Ca2+ channel alpha 1-subunit is expressed in this tissue. Furthermore, only a single splice variant (rbc-II) was observed. The results suggest that a single class of dihydropyridine-sensitive calcium channels regulates inward calcium current in canine colonic smooth muscle cells.
authors.affiliation: Department of Physiology, University of Nevada School of Medicine, Reno 89557.
authors.forename: A
authors.initials: A
authors.lastname: Rich
authors.forename: J L
authors.initials: JL
authors.lastname: Kenyon
authors.forename: J R
authors.initials: JR
authors.lastname: Hume
authors.forename: K
authors.initials: K
authors.lastname: Overturf
authors.forename: B
authors.initials: B
authors.lastname: Horowitz
authors.forename: K M
authors.initials: KM
authors.lastname: Sanders
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015220:Calcium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D003106:Colon / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D004095:Dihydropyridines / Q000494:pharmacology*; D004285:Dogs; D005260:Female; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D009543:Nifedipine / Q000494:pharmacology; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D004095:Dihydropyridines; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine