Elemental composition of sodium-pump inhibited rabbit aorta
vascular smooth muscle cells by electron-probe x-ray
microanalysis.
Krep, Henning, Ann Lefurgey, Steven W. Graves, Daniel Hockett, Peter
Ingram, and Norman K. Hollenberg.
Departments of Medicine and Radiology, Harvard Medical School and
Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115,
The Department of Cell Biology, Duke University Medical Center,
Durham, NC 27710, and Research Triangle Institute, Research Triangle
Park, NC 27709
APStracts 3:0027H, 1996.
The sodium pump in vascular smooth muscle (VSM) is likely to influence
not only intracellular sodium content, but also the content and
distribution of other cations and anions measured by electron probe
x-ray microanalysis (EPXMA). The premise that we tested was that
EPXMA of pump-inhibited vascular smooth muscle would yield a
characteristic cellular elemental profile, providing insight into the
contribution of the sodium pump to the intracellular milieu and an
approach to identifying when VSM operates under the constraints of
pump inhibition. We assessed the contractile state and elemental
EPXMA profile of rabbit aorta that was either quiescent, or
contracted by serotonin (10-6M) or ouabain (10-6M). VSM cytoplasm
showed the anticipated low sodium (28 + 2 mM) and high potassium (182
+ 5 mM) content. With ouabain sodium rose and potassium fell to
reverse the Na:K ratio (0.15 + 0.01 vs. 6.6 + 0.3; P < 0.01).
With serotonin, the ratio rose slightly (0.28 + 0.2; P < .05).
Nuclei and mitochondria showed a similar pattern. Chloride showed a
small increase (56 + 2 to 102 + 4 mM) with ouabain, a shift that
could not be accounted for on the basis of charge redistribution to
maintain neutrality as the change in Na and K were essentially
offsetting. EPXMA measures total and not ionized calcium. If changes
in cytoplasmic calcium occurred, they were too small to be measured
by the imaging methods employed. The sustained, myogenic contractile
response of VSM to sodium pump inhibition shows a characteristic
elemental profile that could prove useful in its identification.
Direct measurement of membrane potential during the myogenic response
to sodium pump inhibition should have a high priority.
Received 22 June 1995; accepted in final form 20 December 1995.
APS Manuscript Number H568-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96