Characterization of binding sites for calcitonin gene related peptide in abalone gill

Target organs for calcitonin gene related peptide were investigated in the abalone. To elucidate the function of this neuropeptide in the biomineraliz ation process, we have localized, in different tissues from abalone, specif ic binding sites for human calcitonin gene related peptide (hCGRP). Highest binding was observed in gill membranes where two classes of affinity compo nents were identified. The affinity constants and the number of binding sit es per mg of proteins for the site I were 5 X 10(9) M-1 and 8.8 x 10(10). F or the site II, the affinity constant was 1.34 x 10(7) M-1 and the number o f binding sites per mg of proteins was 1.1 x 10(12). In contrast, no specif ic calcitonin binding could be detected in every tested tissue, but the sim ilar displacement of the I-125-labeled CGRP binding with unlabeled hCGRP an d sCT suggested that, in the abalone, the identified receptor could belong to a third class receptor subtype, that recognize both hCGRP alpha and sCT. These data suggest that, during evolution, the role of CGRP in gill functi on is particularly well conserved and that this neuropeptide is likely to p articipate in the control of hydromineral metabolism in aquatic species. (C ) 1999 Elsevier Science Inc. All rights reserved.