Extracellular chloride regulates mesangial cell calcium response to
vasopressor peptides.
Stevanovic, Z. S., M. W. Salter, and C. I. Whiteside.
M. R. C. GROUP IN MEMBRANE BIOLOGY, DEPARTMENT OF MEDICINE,
INSTITUTE OF MEDICAL SCIENCE, DIVISION OF NEUROSCIENCE, HOSPITAL FOR
SICK CHILDREN AND DEPARTMENT OF PHYSIOLOGY, UNIVERSITY OF TORONTO,
TORONTO, CANADA
APStracts 3:0006F, 1996.
The role of extracellular chloride in the regulation of mesangial cell
calcium responsiveness to vasopressor peptides was explored. First
the components of vasopressor-stimulated calcium signaling were
defined in rat mesangial cells cultured on coverslips and preloaded
with Fura-2. By spectrofluorometry, manganese uptake (reflecting
divalent cation channel activation) was observed by quenching of
Fura-2, or intracellular cytosolic calcium concentration was
calculated by dual excitation ratiometric measurement. In cells
depolarized with KCl (45 mM), enhanced manganese uptake or increased
cytosolic calcium were inhibited with verapamil (Ver, 10 uM).
Pretreatment of mesangial cells with Ver reduced the sustained
calcium level in response to endothelin-1 (0.1 uM) by 65 +/- 6%
(mean+/-SE, n=12) and to vasopressin (1 uM) by 62 +/- 12% (n=8).
Perforated cell patch-clamp measurement confirmed that endothelin-1
stimulated a sustained increase in cytosolic calcium or divalent
cation entry only in the presence of simultaneous depolarization. In
chloride-free buffer (chloride replaced with the impermeant anions),
sustained calcium response to endothelin-1 was reduced by 72 +/- 8%
(n=8), and by 65 +/- 4% (n=8) in the presence of the chloride channel
inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid (55 uM). In
chloride-free buffer cytosolic calcium (unstimulated) increased to
>200 nM by 30 min. These data indicate that reduced
extracellular chloride increases mesangial cell basal cytosolic
calcium and decreases the transient and sustained cytosolic calcium
response to vasopressor peptides.
Received 17 August 1995; accepted in final form 14 December 1995.
APS Manuscript Number F276-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96