Adenosine transport in perfused rat kidney and renal cortical membrane vesicles

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Abstract
Adenosine is a modulator of renal function but little is known about transport of this compound by renal tubular cells. Transport of exogenous adenosine was studied in isolated perfused rat kidney and in luminal (L) and antiluminal (AL) membrane vesicles isolated from rat renal cortex. Most experiments were performed in the presence of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine. Kidneys were perfused in a recirculating system with Krebs-Henseleit bicarbonate buffer containing 6 g albumin/dl and adenosine. Net secretion of adenosine occurred at perfusate adenosine concentrations greater than 40 microM, and net reabsorption was seen at concentrations less than 40 microM. N6-(L-2-phenylisopropyl)adenosine (PIA), a nondeaminated adenosine receptor agonist, also showed net reabsorption when unbound PIA concentrations were 10-20 microM. Influx or efflux of [3H]adenosine in vesicles was measured using a rapid filtration technique. Transport into both L and AL vesicles was saturable. L vesicles demonstrated both high Km (43 +/- 4 microM) and low Km (4.4 +/- 0.6 microM) transport systems. Only a low Km (5 +/- 1 microM) system could be demonstrated in AL vesicles. Results indicate that at concentrations in the physiological range (less than 1 microM) adenosine undergoes mediated transport across both L and AL membranes and that net transport across the L membrane is in the direction of reabsorption.