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

Although considerable evidence indicates a role for atrial natriuretic factor (ANF) in renal salt regulation, other studies have found a lack of natriuretic response to high-plasma ANF under certain physiological and pathophysiological conditions. The mechanism for this apparent insensitivity to ANF is unknown. In the present study, it was found that ANF binding to its receptor requires the presence of chloride and occurs in a chloride concentration-dependent manner. ANF binding was measured using the purified recombinant 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 presence of NaCl, KCl, or NH(4)Cl. However, binding was undetectable when the salt was replaced with NaHCO(3), CH(3)COONa, or CH(3)COONH(4), indicating that binding requires the presence of chloride. Chloride dependence was also found with the native receptor in bovine adrenocortical membrane preparations. ANF binding 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 approximately 0.6 mmol/L equivalent chloride concentration. Competitive-binding assays at several fixed concentrations of NaCl showed that lowering chloride 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 excess ANF cannot overcome loss of binding caused by low chloride. Chloride-dependent ANF-receptor binding may function as a feedback-control mechanism regulating the ANF-receptor action and, hence, renal sodium excretion.