AJP - Heart and Circulatory Physiology, Vol 271, Issue 2 514-H520, Copyright © 1996 by American Physiological Society
Elemental composition of Na pump inhibited rabbit aorta VSM cells by electron probe X-ray microanalysis
H. Krep, A. Lefurgey, S. W. Graves, D. Hockett, P. Ingram and N. K. Hollenberg
Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA.
The Na pump in vascular smooth muscle (VSM) is likely to influence not only
intracellular Na content but also the content and distribution of other
cations and anions measured by electron probe X-ray microanalysis (EPXMA).
The hypothesis we tested was that EPXMA of pump-inhibited VSM would yield a
characteristic cellular elemental profile, providing insight into the
contribution of the Na 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(-6) M) or ouabain
(10(-6) M). VSM cytoplasm showed the anticipated low Na (28 +/- 2 mM) and
high K (182 +/- 5 mM) content. With ouabain, Na rose and K fell to reverse
the Na-to-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 < 0.05). Nuclei and
mitochondria showed a similar pattern. CI 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 because the
change in Na and K were essentially offsetting. EPXMA measures total and
not ionized Ca. If changes in cytoplasmic Ca occurred, they were too small
to be measured by the imaging methods employed. The sustained, myogenic
contractile response of VSM to Na pump inhibition shows a characteristic
elemental profile that could prove useful in its identification. Direct
measurement of membrane potential during the myogenic response to Na pump
inhibition should have a high priority.
