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Department of Physiology and Laboratory of Cellular and Molecular Physiology, Semmelweis University Medical School, H-1444, Budapest, Hungary
Address all correspondence and requests for reprints to: Dr. András Spät, Department of Physiology, Semmelweis University Medical School, P.O. Box 259, H-1444, Hungary. E-mail: spat{at}puskin.sote.hu
The effect of osmotic changes on aldosterone production, [Ca2+]i and voltage-gated Ca2+ currents, was studied in cultured rat glomerulosa cells. Alteration of osmolarity by sucrose addition in the 250330 mosM range did not influence aldosterone production per se, but it substantially affected K+-stimulated aldosterone production. Hyposmosis markedly increased the hormone response evoked by raising [K+] from 3.6 to 5 mM, whereas hyperosmosis had a mild decreasing effect. Cytoplasmic [Ca2+]i, measured in single glomerulosa cells, did not show detectable change in response to either hyposmotic or hyperosmotic exposure, but the [Ca2+]i signal evoked by elevation of [K+] to 5 mM was augmented in hyposmotic solution. The osmosensitivity of the transient (T)-type and long-lasting (L)-type voltage-gated Ca2+ currents was studied using the nystatin-perforated voltage-clamp technique. Lowering osmolarity to 250 mosM significantly increased the amplitude of the T-type current, and it had a transient augmenting effect on L-type current amplitude. Hyperosmotic solution (330 mosM) reduced L-type current amplitude but did not evoke significant change in T-type current. These results indicate that the responsiveness of rat glomerulosa cells to physiological elevation of [K+] is remarkably influenced by changes in osmolarity by means of modulating the function of voltage-gated Ca2+ channels.
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