Adenosine stimulation of Na+ transport is mediated by an A1 receptor and a [Ca2+]i-dependent mechanism
Authors: John P. Hayslett, Lawrence J. Macala, Joan I. Smallwood, Leena Kalghatgi, Jose Gasalla-Herraiz, Carlos Isales
Journal: Kidney International (1995)

Adenosine stimulation of Na± transport by an A1 receptor and a[Ca2]-dependent mechanism.Studies were performed to determine the primary signal transduction mechanism that mediates adenosine stimulation of electrogenic sodium transport in renal epithelial cells.Experiments were performed on cultured amphibian A6 cells with an adenosine analogue that preferentially binds to the A1 receptor, cyclohexyladenosine (CHA).Sodium transport was assessed by the equivalent short circuit current (Ieq).CHA was found to stimulate Ieq via activation of an A1 receptor because (1) the threshold concentration was 1 n compared to that of 10 J.LM for the specific A2 agonist CGS21680, (2) Cl-lA inhibited vasopressin (AVP)-stimulated cAMP production by a pertussis toxinsensitive mechanism, and (3) the action of CHA was inhibited by the A1 antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX).CHA increased intracellular Ca2 ([Ca2]1) and stimulated phosphoinositide turnover at concentrations that increased Ieq and in a time course that paralleled the increase in Ieq.Ion transport was stimulated by a Ca2-dependent mechanism because the CHA induced increase in Ieq was inhibited by chelating [Ca2I with 5,S'dimethyl BAPTA in a dose-dependent manner, with a K of approximately 10 ILM.The increase in Ieq was also dosedependently inhibited by the specific PKC inhibitors dihydroxychiorpromazine and cheleiythrine, and by trifluoperazine which inhibits PKC and calmodulin.Further studies indicated that Cl-IA-stimulated Ieq was independent of cAMP generation because Cl-IA did not induce an increase in cAMP accummulation parallel to the increase in Ieq in a dose-response analysis, and the adenylate cyclase inhibitor 2',5' dideoxyadenosine (DDA) did not affect the CHA-induced increase in Ieq.These studies indicate, therefore, that adenosine stimulation of Ieq occurs, at least in part, through calcium-dependent signal transduction events and not through regulation of adenylate cyclase.Previous studies established that hormone-stimulated electrogenie sodium transport in renal epithelium results from an increase in apical membrane sodium permeability due to activation or insertion of amiloride-sensitive sodium channels [reviewed in 11.Although pioneer experiments in 1962 suggested that stimulation of electrogenic sodium transport by vasopressin (AVP) was attributable to the second messenger cAMP [2], recent studies indicate that aldosterone-and insulin-stimulated electrogenie transport are in fact mediated by a calcium-dependent mechanism [3,4].The present study was performed to determine the signal transduction system involved in adenosine activation of electrogenie sodium transport.Adenosine is a potent paracoid and autocoid with diverse physiological functions.While studies on its only four to six days after subculture.Experiments were performed 10 to 14 days after subculture, when transmembrane resistance was maximal.Cells were maintained at 27°C in a humidified incubator gassed with 1% C02, and were passaged at intervals of 7 to 10 days.Experiments were performed under sterile conditions in a culture hood.Cell incubations