Proximal tubular Na, Cl, and HCO3 reabsorption and renal oxygen consumption

Abstract

The majority of the oxygen consumed by the rat kidney appears to occur in the proximal tubule. Therefore changes in metabolically linked ion transport in this segment of the nephron should result in changes in renal oxygen consumption. To study the role of bicarbonate reabsorption in metabolically linked proximal tubular ion transport a series of micropuncture-clearance-extraction experiments were performed comparing the effects of the carbonic anhydrase inhibitor benzolamide and of hypertonic sodium bicarbonate infusion with control conditions in the rat. End-proximal tubular fluid and chloride reabsorption were measured. From these, the rates of sodium and bicarbonate reabsorption were estimated. Simultaneously with the tubular fluids, extraction collections were obtained for determination of renal oxygen consumption. Both benzolamide and hypertonic bicarbonate reduced proximal tubular fluid reabsorption while concomitantly reducing the transepithelial gradient for chloride. The mean rate of renal oxygen consumption did not differ from the control rate in either experimental group and could be dissociated from the calculated net rates of proximal tubular sodium, chloride, and bicarbonate reabsorption. We interpret these data as evidence that proximal tubular hydrogen ion secretion supporting bicarbonate reabsorption requires at most small amounts of oxidative energy, less than detectable by these techniques. The data, in contrast, support the conclusion that the chloride-bicarbonate transepithelial gradient appears to be an important passive driving force in vivo for proximal tubular fluid reabsorption.

Role of carbonic anhydrase in acute recovery following renal ischemia reperfusion injury

“…We observed similar decreases in relation to baseline GFR in both groups, while absolute values were lower in the animals receiving CA inhibition. The inhibition of CA had no statistically significant effect on total QO 2 at either baseline or following IR in accordance with previous findings [16]. Since QO 2 was equal in both groups despite GFR being markedly lower after CA inhibition, this resulted in increased QO 2 /TNa indicative of less efficient TNa.…”

Determinants of kidney oxygen consumption and their relationship to tissue oxygen tension in diabetes and hypertension

“…In vitro studies in isolated proximal tubules gave identical results, whereby benzolamide increased Qo 2 and this effect was prevented by inhibition of Na + /H + exchanger isoform 3 and proton secretion . Weinstein et al . had observed similar findings earlier, but attributed the greater Qo 2 to elimination of the chloride gradients that promoted passive reabsorption.…”

Basal renal O2consumption and the efficiency of O2utilization for Na+reabsorption

“…Some studies of the effects of maneuvers that reduced T Na ϩ [e.g., reduced arterial pressure and/or renal blood flow (RBF) or the administration of diuretics] were excluded because of the unavailability of information on GFR and/or TNaϩ (10,11,18,20,26,32,36,37,59,75,78). Others were excluded because GFR was not reduced to zero and T Na ϩ was not measured or because there was no analysis of the relationship between GFR or T Na ϩ and V O 2 total from which basal percent renal V O2 could be derived (1,21,22,25,28,46,50,53,56,63,64,67,76,77) or because no significant correlation was observed between T Na ϩ and V O 2 total (47). We also excluded studies in which both renal V O 2 total and TNaϩ were measured, but the latter were not varied sufficiently to allow the ordinal intercept of the relationship(s) between V O 2 total and TNaϩ or GFR to be determined (7,38), or because the data were not presented in a form to allow this relationship to be extracted (29,42,54).…”