Calcitonin Gene‐Related Peptide‐Binding Sites of Porcine Cardiac Muscles and Coronary Arteries: Solubilization and Characterization

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Abstract
Clacitonin gene-related peptide (CGRP-binding sites were solubilized, using digitonin, from the porcine spinal cord, atria, coronary arteries. The specific binding of 125I-human .alpha.-CGRP to the solubilized binding sites was inhibited by human .alpha.- and .beta.-CGRP and by rat .alpha.-CGRP, but not by angiotensin II or human calcitonin. Scatchard plot analysis of saturation gave the same KD value for CGRP in the crude membrane fractions of the tissues examined. The affinity of CGRP to the binding sites was decreased by solubilization in the atria and coronary arteries, but not in the spinal cord. Affinity labeling followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed distinct molecular sizes of the specific binding sites among the tissues; 70K for the spinal cord, 70K and 90K for the coronary arteries, and 70K and 120K for the atria. These results indicate that the molecular characteristics of the specific binding sites of CGRP in the cardiovascular system are distinct from those in the central nervous system.