Ca2+ release in cultured rat epididymal cells during hypoosmotic swelling

Microfluorimetric studies were carried out to investigate the effects of hypoosmotic swelling on intracellular Ca2+ concentration ([Ca2+]i) in single rat epididymal cells. In Ca(2+)-free solution containing 50 mumols/l ethylenebis(oxonitrilo)tetraacetate (EGTA) hypoosmotic swelling (-160 mosmol/l) induced a transient rise in [Ca2+]i which was either monophasic, biphasic or oscillatory. The [Ca2+]i responses to repeated hypoosmotic stimulations followed a decremental pattern. However, if 2.5 mmol/l Ca2+ was admitted during the recovery period between successive stimulations, the second and the third [Ca2+]i responses were slightly greater than the first. Increasing the change in osmolarity from -14 +/- 1.0 to -154 +/- 1.5 mosmol/l increased the rise in [Ca2+]i but reduced the [Ca2+]i response to subsequent ionomycin stimulation (4 mumols/l). The swelling- and the ionomycin-induced rises in [Ca2+]i followed a reciprocal pattern. It was suggested that intracellular Ca2+ release in response to cell swelling in the epididymal epithelium might play a role in cell volume regulation and the control of epididymal fluid osmolarity.