Abstract
Contractile sensitivity to Ca2+ was studied in rat portal vein circular muscle isolated from normotensive Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). There was no difference in resting membrane potential between WKY and SHRSP. Elevation of extracellular K+ concentration induced similar increase in tension in preparations from WKY and SHRSP. High K+-depolarized preparation developed tension increase when extracellular Ca2+ concentration was increased. The sensitivity to extracellular Ca2+ was similar in preparations from WKY and SHRSP. Permeabilized preparation contracted when free Ca2+ concentration was increased. Sensitivity of permeabilized preparation to Ca2+ was similar in preparations from WKY and SHRSP. These results indicate that regulation of contraction by Ca2+ was similar between WKY and SHRSP. Since there was no change in high K-induced contraction in intact preparations or Cainduced contraction in permeabilized preparations, there seemed to be no difference in Ca2+ influx via voltage-dependent channels in portal vein circular muscle from WKY and SHRSP.
