Mgso4 relaxes porcine airway smooth muscle by reducing ca2+
entry.
Kumasaka, David, Karen S. Lindeman, Judith Clancy, Boris Lande, Thomas
L. Croxton, and Carol A. Hirshman.
Departments of Anesthesiology & Critical Care Medicine and
Environmental Health Sciences, The Johns Hopkins University,
Baltimore, Maryland 21205
APStracts 2:0197L, 1995.
Magnesium sulfate (MgSO4) is used clinically, but its mechanism of
action is unknown. To determine whether MgSO4 relaxes airway smooth
muscle and to investigate the pathways involved, we compared effects
of MgSO4 in porcine tracheal and bronchial muscles contracted with
either carbachol or KCl and measured the effects of MgSO4 on the
concentration of intracellular free calcium ([Ca2+]i). Lungs were
dissected after anesthesia and exsanguination. Tracheal strips and
bronchial rings were suspended in tissue baths for measurement of
isometric tension in the presence of different concentrations of
MgSO4. In separate experiments, tracheal smooth muscle tension and
[Ca2+]i (using the fluorescent dye fura 2) were measured
simultaneously. MgSO4 (1.2, 2.2, 9.2 mM) produced a concentration
-dependent rightward shift of contraction dose-response curves to KCl,
but not to carbachol. MgSO4 relaxed trachealis muscles precontracted
with KCl or carbachol and simultaneously decreased [Ca2+]i. These
findings indicate that MgSO4 directly relaxes airway smooth muscle
and that the mechanism involves a decrease in [Ca2+]i. Because
initiation and maintenance of contraction during KCl stimulation and
maintenance of contraction during carbachol stimulation require Ca2+
entry through voltage-dependent calcium channels, MgSO4-induced
relaxation may involve a decrease in Ca2+ entry via these channels.
Received 5 May 1995; accepted in final form 18 October 1995.
APS Manuscript Number L135-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95