AJP - Cell Physiology, Vol 263, Issue 5 C953-C958, Copyright © 1992 by American Physiological Society
Potentiation of twitch contraction in guinea pig ureter by sodium vanadate
S. Sunano, K. Moriyama and K. Shimamura
Research Institute of Hypertension, Kinki University, Osaka, Japan.
The effect of sodium vanadate on action potential and twitch contraction of
guinea pig ureter was studied and compared with that of ouabain, elevated
K+, low temperature, and a Ca agonist (BAY K 8644), which can be expected
to exert certain comparative effects. Sodium vanadate markedly potentiated
twitch contraction. Potentiation by vanadate was associated with marked
prolongation of relaxation time. Sodium vanadate caused only slight
depolarization of the membrane but marked changes in action potential. The
duration of action potential was prolonged and the number of oscillatory
spike potentials increased. These effects were different from those of
other treatments. It is concluded that prolongation of action potential and
the increase in the number of spikes are the main cause of potentiation of
twitch contraction by sodium vanadate. In addition, inhibition of Ca pump
activity of the smooth muscle membrane system by vanadate might also be
involved in potentiation of twitch contraction.
