Ca2+-Sensitivity of Portal Vein Circular Muscle from Normotensive and Hypertensive Rats.

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 extracel lular 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 influx via voltage-dependent channels in portal vein circular muscle from WKY and SHRSP.

Role of nitric oxide in the contraction of circular muscle in the rat portal vein

“…There was a remarkable difference from previous findings in longitudinal preparations that show rhythmic contractions of low frequency and high amplitude initiated by rhythmic bursts of action potentials [1,12,22,25]. There is little information on the membrane potential of circular muscle of the rat portal vein [23]. In the present study, action potentials appeared sporadically and not in grouped bursts.…”

“…The circular preparation did not show spontaneous rhythmic mechanical activity as has been reported previously [16,23]. There was a remarkable difference from previous findings in longitudinal preparations that show rhythmic contractions of low frequency and high amplitude initiated by rhythmic bursts of action potentials [1,12,22,25].…”

Effects of Flufenamic Acid on Smooth Muscle of the Carotid Artery Isolated from Spontaneously Hypertensive Rats.

“…The solution was equilibrated with a gas mixture of 95% O2 and 5% CO2, and the pH of the solution maintained at 7. Permeabilized preparations of circular muscle of the rat portal vein were made, as described previously (Shimamura et al, 1998). Both ends of a thin strip (50 µm thick, 100 µm wide, 2 mm long) of the circular muscle were tied to tungsten wires with silk thread.…”