AJP - Heart and Circulatory Physiology, Vol 242, Issue 6 967-H972, Copyright © 1982 by American Physiological Society
Effect of tetrodotoxin on membrane potentials and active tone in vascular smooth muscle
J. H. Lombard, M. J. Burke, S. J. Contney, W. J. Willems and W. J. Stekiel
The suitability of tetrodotoxin (TTX) for studies of the neural control of
vascular smooth muscle (VSM) tone in the microcirculation was evaluated by
determining 1) whether TTX blockade of neural input to adrenergically
innervated VSM is reversible and 2) whether TTX depresses active VSM tone
directly. Diameters of rat mesenteric veins and third- and fourth-order
arterioles of the hamster cheek pouch were measured by image splitting. VSM
transmembrane potentials (Em) were measured with microelectrodes in rat
mesenteric veins. In the veins TTX suffusion (10(-6) g/ml) resulted in
dilation and reversible Em hyperpolarization. TTX also reversibly blocked
the venoconstrictor response to perivascular nerve stimulation. TTX had no
effect on the resting tone of hamster arterioles or on arteriolar
constriction in response to increased oxygen availability. TTX did not
affect the response to norepinephrine in either preparation. This study
indicates that TTX specifically and reversibly blocks VSM responses to
neural activation but that it has no direct depressant effect on resting
VSM tone or active constriction in response to nonneural activation.
