Effects of adrenalectomy on CCD: Evidence for diferential response of two cell types

Electrophysiological and chemical methods were used to determine the Na and K transport properties of the isolated cortical collecting duct (CCD) of control and adrenalectomized (ADX) rabbits. Net fluxes of Na (J(Na)) and K (-J(K)) in controls were 5.7 and 3.2 pmol·mm^-1·min^-1 and in ADX were 1.0 and 0.7 pmol·mm^-1·min^-1, respectively, similar to electrically determined rates. In separate experiments, blind impalement of cells from adrenal intact (group 1), ADX (group 2), and ADX rabbits treated with deoxycorticosterone (group 3) allowed identification of two distinct cell types, majority cells (MA) and minority cells (MI). In all groups, MA were distinguished from MI by a relatively high basolateral membrane potential (-V(b)), low apical membrane fractional resistance (FR(a)), and presence of apical and basolateral membrane K conductances. V(b) of MA (-82.4 mV) was significantly hyperpolarized in groups 1 and 3 combined, when compared with group 2 (-66.4 mV). However, there was no significant difference between V(b) of MI group 2 (-38.9 mV) and V(b) of MI in groups 1 and 3 (-36.2 mV). In MA of group 1 equivalent circuit values of apical membrane Na and K conductances (G(a)(Na), G(a)(K)) and maximum pump current (I(max)(p)) were 0.84 and 6.72 mS/cm² and 46.7 μA/cm², respectively. These values in group 2 were significantly lower (0.28 and 1.52 mS/cm² and 8.7 μA/cm², respectively). It is concluded that two cell types can be distinguished electrically in the CCD. MA have properties consistent with principal cells and MI have properties consistent with intercalated cells. ADX causes a decrease in G(a)(Na),G(a)(K), and I(max)(p) of PC that results in proportionate decreases in I(a)(Na) and I(a)(K).