Follicle-stimulating hormone receptor-mediated uptake of 45Ca2+ by cultured rat Sertoli cells does not require activation of cholera toxin- or pertussis toxin-sensitive guanine nucleotide binding proteins or adenylate cyclase.
We have previously reported that FSH stimulates flux of 45Ca2+ into cultured Sertoli cells from immature rats via voltage-sensitive and voltage-independent calcium channels. In the present study, we show that this effect of FSH does not require cholera toxin (CT)- or pertussis toxin (PT)-sensitive guanine nucleotide binding (G) protein or activation of adenylate cyclase (AC). Significant stimulation of 45Ca2+ influx was observed within 1 min, and maximal response (3.2-fold over basal levels) was achieved within 2 min after exposure to FSH. FSH-stimulated elevations in cellular cAMP paralleled increases in 45Ca2+ uptake, suggesting a possible coupling of AC activation to 45Ca2+ influx. (Bu)2cAMP, however, was not able to enhance 45Ca2+ uptake over basal levels at a final concentration of 1000 microM, although a concentration-related increase in androstenedione conversion to estradiol was evident. Exposure of Sertoli cells to CT (10 ng/ml) consistently stimulated basal levels of androstenedione conversion to estradiol but had no effect on basal levels of 45Ca2+ uptake. Similarly, CT had no effect on FSH-induced 45Ca2+ uptake, but potentiated FSH-stimulated estradiol synthesis. PT (10 ng/ml) augmented basal and FSH-stimulated estradiol secretion without affecting 45Ca2+ influx. The adenosine analog N6-phenylisopropyladenosine, which binds to Gi-coupled adenosine receptors on Sertoli cells, inhibited FSH-stimulated androgen conversion to estradiol in a dose-related (1-1000 nM) manner, but FSH-stimulated 45Ca2+ influx remained unchanged. Our results show that in contrast to FSH-stimulated estradiol synthesis, the flux of 45Ca2+ into Sertoli cells in response to FSH is not mediated either directly or indirectly by CT- or PT-sensitive G protein, nor does it require activation of AC. Our data further suggest that the FSH receptor itself may function as a calcium channel.
Grasso
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Department of Biochemistry, Albany Medical College, New York 12208.
Reichert
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D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology*; D004789:Enzyme Activation; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D037342:Pertussis Toxin; D051381:Rats; D011962:Receptors, FSH / Q000187:drug effects / Q000502:physiology*; D012708:Sertoli Cells / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D037361:Adenylate Cyclase Toxin; D002250:Carbon Radioisotopes; D011962:Receptors, FSH; D010566:Virulence Factors, Bordetella; D003994:Bucladesine; D005640:Follicle Stimulating Hormone; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D002118:Calcium