AJP - Cell Physiology, Vol 246, Issue 3 235-C241, Copyright © 1984 by American Physiological Society
Mechanism of action of barium ion on rat aortic smooth muscle
T. R. Hansen, D. X. Dineen and R. Petrak
The mechanism of action of barium ion on the aortic smooth muscle of the
normal rat was investigated using in vitro calcium-depleted aortic strips.
Aortic strips were depleted of calcium by repeated exposure to
norepinephrine in a calcium-free bathing solution. Although calcium
depletion abrogated the response of strips to catecholamines and
depolarizing agents, the response to barium chloride remained
quantitatively intact. The calcium influx blocker D 600 prevented the
contractile response to barium but not to catecholamines, whereas
phentolamine prevented the response to catecholamines but not barium. The
strip response to barium was depressed by a twofold increase in
extracellular magnesium concentration whether the strip was intact or
calcium depleted. Although increased concentrations of calcium in the
extracellular medium inhibited the contractile response to potassium ion,
increases in barium merely potentiated the potassium contracture. These
findings indicate that barium produces its contractile effect on vascular
smooth muscle by a direct intracellular interaction with the contractile or
regulatory proteins. Barium enters these cells via calcium influx channels
and is probably not sequestered in a physiologically releasable pool.
Unlike calcium, barium does not stabilize the smooth muscle sarcolemma when
present in high concentration.
