Effects of antidiuretic hormone on cellular conductive pathways in mouse medullary thick ascending limbs of Henle: I. ADH increases transcellular conductance pathways

Abstract

This paper reports experiments designed to assess the relations between net salt absorption and transcellular routes for ion conductance in single mouse medullary thick ascending limbs of Henle microperfused in vitro. The experimental data indicate that ADH significantly increased the transepithelial electrical conductance, and that this conductance increase could be rationalized in terms of transcellular conductance changes. A minimal estimate (Gminc) of the transcellular conductance, estimated from Ba++ blockade of apical membrane K+ channels, indicated that Gminc was approximately 30-40% of the measured transepithelial conductance. In apical membranes, K+ was the major conductive species; and ADH increased the magnitude of a Ba++-sensitive K+ conductance under conditions where net Cl- absorption was nearly abolished. In basolateral membranes, ADH increased the magnitude of a Cl- conductance; this ADH-dependent increase in basal Cl- conductance depended on a simultaneous hormone-dependent increase in the rate of the net Cl- absorption. Cl- removal from luminal solutions had no detectable effect on Ge, and net Cl- absorption was reduced at luminal K+ concentrations less than 5mM; thus apical Cl- entry may have been a Na+, K+, 2Cl- cotransport process having a negligible conductance. The net rate of K+ secretion was approximately 10% of the net rate of Cl- absorption, while the chemical rate of net Cl- absorption was virtually equal to the equivalent short-circuit current. Thus net Cl- absorption was rheogenic; and approximately half of net Na+ absorption could be rationalized in terms of dissipative flux through the paracellular pathway. These findings, coupled with the observation that K+ was the principal conductive species in apical plasma membranes, support the view that the majority of K+ efflux from cell to lumen through the Ba++-sensitive apical K+ conductance pathway was recycled into cells by Na+, K+,2Cl- cotransport.

Effect of acidosis on chloride transport in the cortical thick ascending limb of Henle perfused in vitro.

“…In these studies chloride transport was reduced and acidosis did not significantly affect chloride transport. Although there appeared to be greater variation in the effect of acidosis on chloride transport in the cTALH in the absence of luminal K, the simplest and most direct interpretation of these results is that chloride reabsorption depends on luminal potassium (consistent with the observations of other investigators 116, [25][26][27]) and that the effect ofan even greater degree ofperitubular acidosis cannot be demonstrated under these conditions. The degree of inhibition of chloride transport in the absence of luminal K is greater in the present study than in previous reports (28).…”

“…Similar effects of acidosis have been reported for the proximal convoluted tubule (24) and the medullary thick ascending limb of Henle (mTALH) (25). Recent work in the mTALH suggests that sodium chloride entry depends on potassium conductance and luminal potassium cotransport (26,27). To examine whether potassium-coupled sodium chloride entry was critical for the inhibition of chloride transport due to acidosis, a separate set of experiments was performed in which luminal potassium was removed.…”

Purification of Ca2+‐activated K+ channel protein on calmodulin affinity columns after detergent solubilization of luminal membranes from outer renal medulla

“…Mops, 3-(N-morpholino)-propanesulfonic acid; PMSF, phenylmethylsulfonyl fluoride; TAL, thick ascending limb of Henle's loop; TFP, trifluoperazine luminal membrane together with the Na+,K+ pump and a net Cl-conductance in the basolateral membrane [1,2]. The K+ channel is stimulated by Ca*+ in physiological concentrations [3,4] and may thus be involved in regulation of transepithelial NaCl transport.…”

Cyclic guanosine monophosphate is the mediator of platelet-activating factor inhibition on transport by the mouse kidney thick ascending limb.

“…TAL is involved in two main reabsorptive functions which are sodium chloride reabsorption, contributing to the generation of the corticopapillary gradient, and the reabsorption of the bulk of the filtered calcium and magnesium. Since chloride transport has been shown to be closely correlated to sodium transport as well as to the passive reabsorption of the divalent cations (8,9), Jcl, determined on microperfused tubules, was used as the representative parameter of the TAL function. The fact that, in the present study, the inhibitory effect of PAF on Jcl was found to be similar in the cortical TAL (cTAL) and in the mTAL allowed us to investigate the mechanism of action involved in this effect on either segment.…”