AJP - Cell Physiology, Vol 251, Issue 5 687-C695, Copyright © 1986 by American Physiological Society
Influence of altering cellular magnesium content on vascular smooth muscle contractility
G. D. Ford and S. P. Driska
Tissue and cellular Mg levels in porcine carotid arterial strips were
varied by 4-h incubation in high-K+, Ca2+-free solutions containing
variable amounts of MgCl2 (0, 0.6, 1.2, 3, 5, 10, and 15 mM). The total Mg
content, designated tissue Mg, was determined immediately after the
incubation and also 1 and 3 h after reexposure to a normal physiological
salt solution (PSS) containing 1.2 mM Mg2+. Cellular Mg levels were
calculated from this data. The tissue Mg was profoundly altered immediately
following the incubation, with values ranging from 7.3 mumol/g dry wt to
71.4 mumol/g dry wt, but remained significantly elevated following
reexposure to normal PSS only in those strips incubated in 15 mM Mg2+. The
calculated cellular Mg levels, however, did remain significantly elevated
if 1 microM ouabain was included in both the incubation and post-incubation
solutions. The response to high K+ in tissues subjected to the same 4-h
incubation procedure exhibited the same pattern as the cellular Mg levels.
Postincubation changes in the response to norepinephrine, either in the
presence or absence of external Ca2+, depended on both the dose of
norepinephrine and the level of Mg2+ in the incubation medium. It appears
sarcoplasmic Mg levels are capable of modulating arterial contractility
through influences at both the level of contractile proteins and the
delivery of activator Ca2+.
