Binding Sites for Islet Amyloid Polypeptide in Mammalian Lung: Species Variation and Effects on Adenylyl Cyclase.

Islet amyloid polypeptide (IAPP) and calcitonin gene related peptide (CGRP) share a 47% sequence homology. IAPP can interact with adenylyl cyclase coupled CGRP receptors. We have examined [125I]IAPP binding in mouse, pig, and guinea pig lung membranes in competition with IAPP, CGRP, and CGRP(8–37). Three types of site were shown by order of potency: (i) mouse, IAPP > CGRP(8–37) [Formula: see text] CGRP; (ii) pig, CGRP > IAPP > CGRP(8–37); and (iii) guinea pig, CGRP = IAPP = CGRP(8–37). Chemical cross-linking of [125I]IAPP and [125I]CGRP binding sites in lung demonstrated that both sites had similar molecular weights in any one species but differed across species, i.e., mouse Mr = 70 000 and 98 000; pig Mr = 68 000, 56 000, and 47 000; and guinea pig Mr = 106 000 and 56 000. Adenylyl cyclase activity was stimulated by forskolin and AlCl3–NaF in rat, mouse, pig, and guinea pig membranes. Only in mouse and pig were CGRP and IAPP able to stimulate adenylyl cyclase activity. In mouse lung CGRP and IAPP stimulated adenylyl cyclase activity with EC50 values of 642 ± 222 nM (n = 4) and 325 ± 115 nM (n = 4), respectively. In pig lung membranes EC50 values were 5.7 ± 0.3 nM (n = 4) for CGRP and 1230 ± 1130 nM (n = 4) for IAPP. Thus IAPP either did not stimulate adenylyl cyclase activity in these lung membranes or did so with a low potency.Key words: islet amyloid polypeptide, amylin, calcitonin gene related peptide, lung, receptors.