Coupling of active ion transport and aerobic respiratory rate in isolated renal tubules.

Abstract

We report the results of studies in which the cytoplasmic coupling between Na+,K+-ATPase activity (presumably a measure of active transport) and the mitochondrial respiratory rate was investigated in a tubule suspension from the rabbit kidney cortex. Simultaneous measurements of the redox state of mitochondrial nicotinamide adenine dinucleotide (NAD) (performed fluorometrically), the cellular ATP and ADP concentrations, and the oxygen consumption rate (Qo) were made under conditions known to alter the Na+,K+-ATPase turnover. Ouabain (25 AM) caused: (i) a 54% inhibition of Qo2,(ii) a net reduction of NAD, and (iii) a 30% increase in the ATP/ADP ratio. The addition of K+ (5 mM) to K+-depleted tubules caused: (i) an initial 127% stimulation of Qo2 followed by a new steady-state Qo2 50% above control, (ii) an initial large oxidation of NAD followed by a new steady state more oxidized than the control level, and (iii) a 47% decrease in the cellular ATP/ADP ratio. These data indicate that the cellular ATP and ADP concentrations or the ATP/ADP ratio may be part of the coupling mechanism linking Na+,K+-ATPase turnover and the aerobic metabolic rate in kidney.A basic question in cellular physiology concerns the mechanism whereby the rate of aerobic conversion of energy is coupled to the rate of active ion transport. A linear relationship between the rate of oxygen consumption and active sodium transport has been observed in numerous epithelia such as frog skin (1), toad bladder (2), and kidney (3, 4), indicating a close link between these two processes. Because Na+,K+-ATPase appears to be either directly or indirectly involved in most active sodium transport processes (5, 6), it is generally accepted that ATP is the most likely energy source for sodium transport. However, it is still unclear how changes in transport rate elicit corresponding alterations in aerobic respiration. Attempts to answer this question have focused on the role of the cellular concentrations of ATP, ADP, and orthophosphate (Pi), or a combination of these variables to express a phosphate potential (7,8) or energy charge (9), in controlling the mitochondrial respiratory rate. In theory, an increase in active ion transport would cause an increase in the rate of ATP hydrolysis, which would be expected to elicit a decrease in the cellular concentration of ATP and an increase in the concentration of the ATP hydrolysis products, ADP and P1. In a model suggested by Whittam and coworkers (10, 11), such an increase in ADP and Pi concentrations could serve as a cytoplasmic feedback signal resulting in an acceleration of the mitochondrial respiratory rate, as described for isolated mitochondria by Chance and Williams (12). We present here experiments performed on an isolated cortical tubule suspension from the rabbit (21), which is ideally suited to test directly the role of ATP and ADP concentrations and the ATP/ADP ratio in the coupling of cellular respiration to cellular ion transport. This preparation contains little glomerular contamination, is no...

Intracellular respiratory dysfunction and cell injury in short-term anoxia of rabbit renal proximal tubules.

“…By subjecting the kidney to ischemia of varying duration, investigators have been able to describe the many morphologic, physiologic, and biochemical alterations that occur in the kidney as a function of time (1)(2)(3)(4)(5)(6) Receivedfor publication 25 March 1985 and in revisedform 28 August 1985. oxygen, proximal tubules rapidly lose K and gain Na (7,8), and decrease their ATP content (9,10). Within 15 min of clampinduced ischemia, structural alterations are clearly observed in the form of cellular and mitochondrial swelling and irregular brush borders (10, 1 1).…”

ATP depletion in rat cholangiocytes leads to marked internalization of membrane proteins

“…Transporting epithelia expend approximately 50% of their metabolic output to maintain the intracellular ionic environment and to support vectorial movement of water, ions, and solutes. 27 Membrane and transporter internalization would reduce the ionic permeability of the membrane and lessen the required metabolic resources needed to defend the intracellular ionic environment. With regards to recovery, however, the internalization did not serve to promote the rapid restoration of either structure or function because both remained impaired for extended periods (Figs.…”

Inhibition of Renal Metabolism. Relative effects of arsenate on sodium, phosphate, and glucose transport by the rabbit proximal tubule.

“…5 shows a representative study from this series. The addition of ouabain decreased the rate of oxygen consumption and increased NADH fluorescence (22). The subsequent addition of arsenate increased oxygen consumption and decreased NADH fluorescence more dramatically than in Fig.…”

“…4 cence (15%). The simultaneous increase in oxygen consumption and decrease in NADH fluorescence are consistent with the uncoupling of oxygen consumption from the phosphorylation of ADP to ATP (8,21,22) and with the stimulation of cellular ATPase activity (22). To distinguish these two possibilities, we repeated the studies in the presence of 0.5 mM ouabain to inhibit sodium-potassium ATPase activity totally, and thereby decrease the respiratory rate of the tissue.…”

“…Two types of conditions would elicit these responses in isolated mitochondria; either a transition to a more active state that would stimulate respiration and increase the rate of ATP production, or an uncoupling action that would stimulate respiration bust would inhibit ATP production (21,22,24). The first response might have occurred if arsenate increased the rate of ATP use but this seems unlikely because arsenate decreased net sodium transport, a major pathway for the use of ATP (25,26).…”