REGULATION OF INTRACELLULAR PH IN 2 CELL-POPULATIONS OF INNER STRIPE OF RABBIT OUTER MEDULLARY COLLECTING DUCT

The inner stripe of the outer medullary collecting duct (OMCD(is)) is a major site of HCO3- reabsorption and urinary acidification. Whether this nephron segment consists of a single or multiple cell types remai ns unclear. Apical incubation of rabbit OMCD(is) via luminal perfusion with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester resulted in heterogeneous fluorescence, suggesting two cell type s. This heterogeneity was not prevented by inhibition of either carbon ic anhydrase or organic anion transport. Subsequent studies were direc ted at characterizing the major intracellular pH (pH(i)) regulatory tr ansporters in these two cell populations. Both cell populations demons trated similar rates of Na+/H+ exchange, as assessed by peritubular Na +-dependent, amiloride-sensitive pH(i) recovery from an intracellular acid load. In contrast, Na+-independent, HCO3--independent pH(i) recov ery from an acid load was present in both cell populations but had two to three times greater activity in a minority cell population. In viv o deoxycorticosterone acetate administration increases this rate in bo th populations but to a greater extent in the minority cell population . In CO2/HCO3--containing solutions, Cl- removal from the peritubular solution caused 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensi tive alkalinization of all cells. Again, the magnitude and rate of alk alinization were significantly greater in the minority cell population . These studies demonstrate that the OMCD(is) consists of qualitativel y similar cells in different states of functional activity. Although t hey are similar in most characteristics, a minority of cells more acti vely secrete H+ (independent of Na+) and reabsorb HCO3-.