AJP - Cell Physiology, Vol 264, Issue 6 C1388-C1394, Copyright © 1993 by American Physiological Society
ATP stimulates Ca2+ release from a rapidly exchanging pool in cultured rat epididymal cells
A. Y. Leung, H. L. Tai and P. Y. Wong
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, New Territories.
A study was carried out to investigate an ATP-sensitive Ca2+ pool in rat
epididymal cells and its role in transepithelial Cl- secretion. In normal
buffered solution containing 2.5 mM free Ca2+, ATP triggered single calcium
spikes in a dose-dependent fashion. In nominally Ca(2+)-free solution, the
peaks of successive Ca2+ spikes diminished after repeated ATP stimulations.
Addition of Sr2+ (2.5 mM) to Ca(2+)-free solution after ATP stimulation did
not cause changes in fluorescence signals. However, in the presence of
Sr2+, ATP gave rise to apparent repetitive Ca2+ spikes of similar
magnitudes after repeated stimulations. Increasing the time of exposure in
Ca(2+)-free solution containing 50 microM ethylene
glycol-bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid rapidly
decreased the intracellular Ca2+ concentration ([Ca2+]i) response to
subsequent ATP stimulation. On the other hand, increasing the time of
exposure in Sr(2+)-containing solution in Ca(2+)-depleted cells rapidly
increased the apparent [Ca2+]i response to subsequent ATP stimulation.
These observations suggested the existence of a Ca2+ pool that was rapidly
exchanging with the extracellular compartment. Apical application of ATP
elicited a transient rise in short-circuit current across the epididymal
epithelium in a dose-dependent fashion, and the response was reduced by
prior stimulation with thapsigargin. Ca2+ released from a rapidly
exchanging ATP-sensitive store might stimulate Cl- secretion in the
epididymis, thereby maintaining the electrolyte contents and fluidity of
the epididymal microenvironment.
