Requirement for transmembrane sodium flux in maintenance of cytosolic calcium levels in rat Sertoli cells.
The prompt rise in cytosolic calcium induced by follicle-stimulating hormone (FSH) in rat Sertoli cells suggests a role for calcium in FSH signal transduction. To evaluate the requirement for sodium in transmembrane calcium fluxes in Sertoli cells, we measured intracellular calcium concentration under sodium-free conditions and during stimulation by monensin and veratridine, used to elevate cytosolic sodium. Cytosolic calcium levels were measured by dual-wavelength spectrofluorimetry using freshly isolated cells loaded with fura-2 acetoxymethyl ester. Whereas, removal of extracellular sodium lowered cytosolic calcium in unstimulated cells from 89 +/- 4 to 75 +/- 8 nM, treatment with monensin and veratridine increased cytosolic calcium to 142 +/- 19 and 126 +/- 13 nM, respectively. Without extracellular calcium, monensin still produced 47% of the rise in cytosolic calcium observed in the presence of extracellular calcium, indicating approximately equal contributions of calcium from intracellular and extracellular sources. Blockade of voltage-sensitive or/and voltage-insensitive calcium channels by verapamil and ruthenium red was unable to completely prevent the monensin-induced elevation of cytosolic calcium. In addition tetrodotoxin failed to block the FSH-induced rise in cytosolic calcium. These observations, together with the considerable reduction in monensin-induced rise in cytosolic calcium under extracellular sodium-free condition, support the hypothesis that sodium-calcium exchange rather than the specific calcium or sodium channels regulate basal and monensin-induced transmembrane sodium and calcium fluxes in Sertoli cells.
Department of Obstetrics and Gynecology, University of Sydney, New South Wales, Australia.
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E
Gorczynska
D J
DJ
Handelsman
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D003600:Cytosol / Q000378:metabolism*; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008985:Monensin / Q000494:pharmacology; D051381:Rats; D012146:Rest; D012708:Sertoli Cells / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D003470:Culture Media; D015222:Sodium Channels; D013779:Tetrodotoxin; D005640:Follicle Stimulating Hormone; D008985:Monensin; D012964:Sodium; D002118:Calcium