Benzamil binding to kidney cell membranes

Abstract

Tile binding of [ 3H]benzamil ( N-benzylamidino-3,5-diamino-6-chloropyrazine carboxamide), a blocker of passive sodium channels, was investigated in tissues from several species (rat, guinea-pig, rabbit, chicken, frog and two species of fish). Tissues used were kidney, colon epithelium, cardiac and skeletal muscle, brain, liver, epididymis and red cell membranes. Displaceable binding was detected principally in target tissues, and particularly in the kidney. In rat and rabbit kidney considerably more binding activity was present in the cortex than in the medulla. In rat kidney cortex, a saturable binding component (2 nmoles g −1 protein) with high affinity (approx. 5 × 10 7 M −1) was detected. Other agents which are known to interact with sodium channels competed with [ 3H]benzamil for the binding site. The affinity of amiloride detected in this way was 10 5 M −1. Neither adrenalectomy nor pretreatment with aldosterone affected the amount of benzamil binding activity. Sodium had no effect on either the affinity or the capacity of binding. The binding activity appeared not to be associated with the base carrier known to be present in the proximal convoluted tubule. Binding activity was increased in both crude plasma membrane fractions and in fractions enriched in brush border membranes. The possible physiological role of the diuretic receptor is discussed.