Atp-mediated calcium signaling in preglomerular smooth muscle
cells.
Inscho, Edward W., Ph. D., Alan C. Schroeder, M. P. H., Paul C.
Deichmann, B. S. and John D. Imig, Ph. D.
Department of Physiology, Tulane University School of Medicine, New
Orleans, LA 70112
APStracts 5:0202F, 1998.
Studies were performed to determine the effect of extracellular ATP on
the intracellular Ca2+ concentration ([Ca2+]i) in freshly isolated
microvascular smooth muscle cells (MVSMC). Suspensions of
preglomerular MVSMC were prepared by enzymatic digestion and loaded
with fura 2. Single cells were studied using a microscope-based
fluorescence spectrophotometer during superfusion of a physiological
salt solution with 1.8mM Ca2+ and during exposure to similar
solutions containing ATP. Under control conditions, baseline [Ca2+]i
averaged 107 [angstrom]a 6nM (n=86 cells from 34 animals). ATP
administration elicited concentration-dependent increases in [Ca2+]i.
Exposure to ATP concentrations of 1, 10 and 100_M increased
intracellular calcium to peak concentrations of 133 [angstrom]a 20,
338 [angstrom]a 37 and 367 [angstrom]a 35nM; respectively (P<0.05
vs respective baseline). Steady state [Ca2+]i increased to 113
[angstrom]a 15; 150 [angstrom]a 16 (P<0.05 vs baseline) and 180
[angstrom]a 12nM (P<0.05 vs baseline) for the same groups. The
[Ca2+]i response to ATP was also assessed in the absence of
extracellular Ca2+ and during blockade of L-type calcium channels
with diltiazem. In these studies, exposure to 100_M ATP induced a
transient peak increase in [Ca2+]i with the plateau phase being
totally abolished under calcium free conditions and markedly
attenuated during calcium channel blockade; respectively. These data
indicate that ATP-mediated P2 receptor activation increases [Ca2+]i
in freshly isolated preglomerular MVSMC by stimulating Ca2+ release
from intracellular stores in addition to stimulating the influx of
extracellular Ca2+ through voltage-gated L-type calcium channels.
Received 19 August 1998; accepted in final form 13 November 1998.
APS Manuscript Number F214-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 20 November 1998