title: Ba2+ and K+ alteration of K+ conductance in spontaneously active vascular muscle.
abstract: The spontaneous spiking of vascular muscle in hepatic portal vein was converted from a burst pattern to single spiking by K+ concentrations greater than 20 mM. A pronounced decrease in contraction amplitude was always associated with the conversion of bursts of spikes to single spikes. The single spikes were accompanied by contractions that were only 1-5% of the magnitude of the contractions associated with spike bursts. Ba2+ (1 mM) increased the number of spikes per burst in myovascular cells at low(less than 10 mM) K+ concentrations. Even though Ba2+ caused depolarization, which itself tended to cause conversion to single spiking, the number of spikes per burst and contraction amplitude were greater in Ba2+ solutions. The slope of the Em-log [K+]o relationship depended on the time allowed for changes in [K+], and a maximum slope of 36 mV/decade and an extrapolated [K+]i of 160 mM were the highest slope and lowest [K+]i values recorded. Ba2+ slightly decreased (to 28 mV/decade) the slope of the curve but did not alter the intercept at [K+] = 160 mM. Ba2+ caused an increase in input resistance (rin) and depolarization independent of CL- concentration, and thus appeared to decrease K+ conductance. K+ concentration increases tended to increase K+ conductance (decrease rin) with depolarization. Spontaneously active vascular muscle thus appears to have a K+ conductance that can be altered and to show different spike patterns and altered conduction, resulting in a marked change in contractions. The spike pattern appears to depend at least partially on the combination of K+ conductance and Em.
mesh_terms: D000818:Animals; D001464:Barium / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000502:physiology*; D009467:Neuromuscular Depolarizing Agents; D011169:Portal Vein / Q000502:physiology; D011188:Potassium / Q000494:pharmacology / Q000502:physiology*; D051381:Rats
chemical_list: D009467:Neuromuscular Depolarizing Agents; D001464:Barium; D011188:Potassium