Heterogeneity of the rabbit collecting tubule: Localization of mineralocorticoid hormone action to the cortical protein

Abstract

This study was designed to examine the sodium, potassium, and chloride transport rates across the cortical and outer medullar collecting tubule and to localize the action of mineralocorticoid hormone. Rabbit collecting tubules were dissected from the cortex (CCT), the outer stripe of the outer medulla (OMCT(o)), or the inner stripe of the outer medulla (OMCT(i)). From normal rabbits, the transepithelial voltage was -20.8±2.7 mV in CCT, -4.2±1.4 mV in OMCT(o), and +10.6±2.3 mV in OMCT(i). From DOCA-treated rabbits, only the CCT voltage was different (-42.9 mV). Net sodium absorption across the CCT increased with DOCA-treatment from 23±5 to 54±8 pEq.mm-1.min-1, whereas net potassium secretion increased from 15±2 to 43±5 pEq·mm-1·min-1. Net chloride absorption was significant only in DOCA-treated rabbits. The OMCT(i), in contrast, displayed no net transport of sodium, potassium, or chloride and had a lower rate coefficient for sodium efflux than did the CCT. DOCA treatment had no effect on any transport rate measured in this segment. The OMCT(o) had small potassium secretion, which did not increase with DOCA treatment. The collecting tubule is heterogeneous along its length with respect to ion transport. Mineralocorticoid-hormone-sensitive sodium absorption is present predominantly, if not exclusively, in the cortical collecting tubule.