A new role for follicle-stimulating hormone in the regulation of calcium flux in Sertoli cells: inhibition of Na+/Ca++ exchange.
Elucidation of mechanisms regulating intracellular calcium levels in steroidogenic tissues is important for understanding control of cellular function. We have previously described FSH receptor-mediated flux of 45Ca++ into cultured rat Sertoli cells and receptor-enriched proteoliposomes via voltage-sensitive and voltage-independent calcium channels. In the present study, we report heretofore unrecognized inhibitory effects of FSH on Na+/Ca++ exchange in these two systems. An outwardly directed Na+ gradient, developed by preincubating Sertoli cell monolayers in buffer made hypertonic with NaCl, resulted in uptake of 45Ca++ that was unaffected by calcium channel blocking agents, ruthenium red or methoxyverapamil, but was enhanced by ouabain, a specific inhibitor of Na+/K(+)-ATPase. Sodium-dependent 45Ca++ flux into Sertoli cells was inhibited in a concentration-related manner by increased extracellular Na+ (up to 135 mM). FSH consistently and reproducibly (28.9 +/- 3.8%, 10 separate assays) reduced sodium-dependent 45Ca++ influx in the absence or presence of ouabain. A lesser effect on Na+/Ca++ exchange was seen when Li+ replaced Na+ in the preincubation buffer, and a marked reduction occurred when Sertoli cells were incubated in buffer containing KCl, presumably due to membrane depolarization. FSH-sensitive Na+/45Ca++ exchange was also observed when using FSH receptor-enriched proteoliposomes. Our earlier calcium channel studies indicated that FSH affects Ca++ entry into Sertoli cells via a receptor-mediated process. The results reported here demonstrate that the interaction of FSH with its receptor is associated with changes in Na+/Ca++ exchange as well, and suggest that this activity may also be involved in regulating intracellular free Ca++ levels in the Sertoli cell.
Grasso
P
P
Department of Biochemistry, Albany Medical College, New York 12208.
Joseph
M P
MP
Reichert
L E
LE
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D007700:Kinetics; D008081:Liposomes; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D010713:Phosphatidylcholines; D011510:Proteolipids / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011962:Receptors, FSH / Q000378:metabolism; D012708:Sertoli Cells / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013737:Testis / Q000378:metabolism
D002132:Calcium Radioisotopes; D008081:Liposomes; D010713:Phosphatidylcholines; D011510:Proteolipids; D011962:Receptors, FSH; C020485:proteoliposomes; D010042:Ouabain; D005640:Follicle Stimulating Hormone; D012964:Sodium; C017251:1,2-oleoylphosphatidylcholine; D002118:Calcium