Atrial natriuretic factor binding to its receptor is dependent on chlorideconcentration - A possible feedback-control mechanism in renal salt regulation

Although considerable evidence indicates a role for atrial natriuretic fact or (ANF) in renal salt regulation, other studies have found a lack of natri uretic response to high-plasma ANF under certain physiological and pathophy siological conditions. The mechanism for this apparent insensitivity to ANF is unknown. In the present study, it was found that ANF binding to its rec eptor requires the presence of chloride and occurs in a chloride concentrat ion-dependent manner. ANF binding was measured using the purified recombina nt hormone-binding domain of the ANF receptor in the presence of 0.1 mol/L NaCl or other selected salt. High specific binding was detected in the pres ence of NaCl, KCl, or NH4Cl. However, binding was undetectable when the sal t was replaced with NaHCO3, CH3COONa, or CH3COONH4 indicating that binding requires the presence of chloride. Chloride dependence was also found with the native receptor in bovine adrenocortical membrane preparations. ANF bin ding to the recombinant protein was chloride concentration-dependent over a range from 0.05 to 10 mmol/L and a half-maximum binding was attained at ap proximate to 0.6 mmol/L equivalent chloride concentration. Competitive-bind ing assays at several fixed concentrations of NaCl showed that lowering chl oride concentration caused a decrease in maximum binding but did not alter K-d values, suggesting that a loss of chloride turns off ANF binding rather than reducing affinity for ANF. Saturation-binding studies showed that exc ess ANF cannot overcome loss of binding caused by low chloride. Chloride-de pendent ANF-receptor binding may function as a feedback-control mechanism r egulating the ANF-receptor action and, hence, renal sodium excretion.