A tetrapeptide within a receptor-binding region of human follicle-stimulating hormone beta-subunit, hFSH-beta-(34-37), regulates sodium-calcium exchange in Sertoli cells

Abstract

In a previous study, we showed that binding of FSH by cultured rat Sertoli cells significantly inhibited basal levels of Na+/Ca2+ exchange. Similar inhibition was observed when proteoliposomes enriched with bovine calf testis follicle-stimulating hormone (FSH) receptors were stimulated with FSH. In the present study, we screened a series of overlapping synthetic peptide amides, representing the entire primary structure of the beta-subunit of hFSH, for their effects on sodium-dependent calcium uptake (as 45Ca2+) by monolayer cultures of Sertoli cells from immature rats. hFSH-beta-(33-53), previously identified as a receptor binding region of hFSH-beta-subunit, significantly (P < 0.05) inhibited Na+/Ca2+ exchange. A tetrapeptide [TRDL, hFSH-beta-(34-37)] contained within this sequence, was observed to be equally as active as hFSH-beta-(33-53) at 200 microM, suggesting that the regulatory effect of hFSH-beta-(33-53) on sodium-dependent 45Ca2+ influx was due to residues 34-37. hFSH-beta-(81-95) also inhibited Na(+)-dependent calcium influx, although to a lesser extent than hFSH-beta-(33-53) or hFSH-beta-(34-37). Sodium-dependent 45Ca2+ entry into Sertoli cells was enhanced in a concentration-related manner when extracellular sodium was replaced by equimolar concentrations (up to 135 mM) of choline chloride. hFSH-beta-(34-37) significantly reduced basal uptake of 45Ca2+ in choline-containing buffer, but was without effect in buffer containing 135 mM NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)