Atrial peptides inhibit oxygen consumption in kidney medullary collecting duct cells

Atrial natriuretic peptides (ANP) stimulate renal Na+ excretion by poorly understood mechanisms, perhaps involving direct inhibition of Na+ transport in the kidney medulla. To examine the effects of ANP on renal cells directly, we prepared highly purified cell suspensions derived from inner and outer medullary collecting duct and thick ascending limb of rabbit kidney and monitored ouabain-sensitive oxygen consumption (QO2). Human ANP diminished QO2 by 27.4 +/- 1.6% (mean +/- SE) in inner medullary collecting duct cells but had no effect in cells derived from outer medullary collecting duct or thick ascending limb. The inhibitory effect of ANP was not additive with either amiloride or ouabain. ANP was without effect in the presence of amphotericin. These results indicate that ANP inhibited Na+ entry in inner medullary collecting duct cells. ANP-mediated inhibition of QO2 was dose dependent (Ki = 5.5 X 10(-10) M) and exhibited selectivity for peptide structure. These results suggest that atrial peptides enhance renal sodium excretion partly by direct inhibition of medullary collecting duct sodium transport.