Synthetic peptides corresponding to human follicle-stimulating hormone (hFSH)-beta-(1-15) and hFSH-beta-(51-65) induce uptake of 45Ca++ by liposomes: evidence for calcium-conducting transmembrane channel formation.
We have previously described FSH receptor-mediated influx of 45Ca++ in cultured Sertoli cells from immature rats and receptor-enriched proteoliposomes via activation of voltage-sensitive and voltage-independent calcium channels. We have further shown that this effect of FSH does not require cholera toxin- or pertussis toxin-sensitive guanine nucleotide binding protein or activation of adenylate cyclase. In the present study, we have identified regions of human FSH-beta-subunit which appear to be involved in mediating calcium influx. We screened 11 overlapping peptide amides representing the entire primary structure of hFSH-beta-subunit for their effects on 45Ca++ flux in FSH receptor-enriched proteoliposomes. hFSH-beta-(1-15) and hFSH-beta-(51-65) induced uptake of 45Ca++ in a concentration-related manner. This effect of hFSH-beta-(1-15) and hFSH-beta-(51-65) was also observed in liposomes lacking incorporated FSH receptor, suggesting that the peptide amides may act as ionophores or channel-formers. Reducing membrane fluidity by incubating liposomes (containing no receptor) with hFSH-beta-(1-15) or hFSH-beta-(51-65) at temperatures lower than the transition temperatures of their constituent phospholipids resulted in no significant (P greater than 0.05) difference in 45Ca++ uptake. The effectiveness of the calcium ionophore A23187, however, was abolished. Ruthenium red, a voltage-independent calcium channel antagonist, was able to completely block uptake of 45Ca++ induced by hFSH-beta-(1-15) and hFSH-beta-(51-65) whereas nifedipine, a calcium channel blocker specific for L-type voltage-sensitive calcium channels, was without effect. These results suggest that in addition to its effect on voltage-sensitive calcium channel activity, interaction of FSH with its receptor may induce formation of transmembrane aqueous channels which also facilitate influx of extracellular calcium.
Grasso
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P
Department of Biochemistry, Albany Medical College, New York 12208.
Santa-Coloma
T A
TA
Reichert
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LE
D000577:Amides / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002132:Calcium Radioisotopes; D005640:Follicle Stimulating Hormone / Q000138:chemical synthesis / Q000494:pharmacology*; D037201:Follicle Stimulating Hormone, beta Subunit; D006801:Humans; D008081:Liposomes / Q000378:metabolism*; D008560:Membrane Fluidity; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000494:pharmacology*; D010713:Phosphatidylcholines / Q000138:chemical synthesis / Q000494:pharmacology*
D000577:Amides; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002132:Calcium Radioisotopes; D037201:Follicle Stimulating Hormone, beta Subunit; D008081:Liposomes; D010446:Peptide Fragments; D010713:Phosphatidylcholines; C068938:follicle stimulating hormone, beta subunit (51-65); C068939:follicle stimulating hormone, beta subunit (1-15); C068738:1-palmitoyl-2-parinaroylphosphatidylcholine; D005640:Follicle Stimulating Hormone; D002118:Calcium