Regulation of the atrial natriuretic peptide receptor on a smooth muscle cell

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Abstract
We have used a smooth muscle cell line isolated from rabbit carotid artery (RCA) as a model system with which to study the ligand-mediated regulation of the atrial natriuretic peptide (ANP) receptor. RCA cells bind rat alpha-ANP-(1-28) semi-irreversibly at 4 degrees C, apparently to a single class of high-affinity binding sites (Kd approximately equal to 5 pM). In contrast, ANP initially bound to RCA cells at 37 degrees C is fully reversible after the cells have been cooled to 4 degrees C. Although the measured dissociation constant for binding rat alpha-ANP-(1-28) is 10-fold lower at 4 degrees C than at 37 degrees C, the maximum amount of specifically bound radioligand is equivalent at both temperatures. We infer this to be suggestive of ANP receptor recycling occurring at 37 degrees C. This hypothesis is substantiated by experiments demonstrating the rapid disappearance of ANP receptors (measured at 4 degrees C) after exposure of RCA cells to ANP at 37 degrees C. We believe this reflects a loss of cell-surface receptors that is reversible on removal of ANP from the incubation medium at 37 degrees C. The concentration dependence and rank order of potency of ANP in eliciting receptor redistribution resembles that for binding to the ANP receptor and not for eliciting cyclic GMP formation. In contrast to this striking loss of presumed cell-surface receptors, incubation of RCA cells with ANP elicits only limited desensitization of the cyclic GMP response.(ABSTRACT TRUNCATED AT 250 WORDS)