Adenosine stimulates sodium transport in kidney A6 epithelia in culture

Abstract

The effects of adenosine receptor agonists and antagonists were examined in epithelia formed in culture by A6 cells, a continuous cell line derived from Xenopus laevis kidney. A6 epithelia have a high electrical resistance and a short-circuit current that is equal to net sodium flux from mucosal to serosal surface. Adenosine, 2-chloroadenosine, 5'-(N-ethyl)carboxamidoadenosine, and N6-(L-2-phenylisopropyl) adenosine produced concentration-dependent increases in short-circuit current. Stimulation of short-circuit current by 2-chloroadenosine occurred at concentrations of 0.05 microM and above, with half-maximal stimulation occurring at 0.3 microM. 5'-(N-ethyl)carboxamidoadenosine was more potent than N6-(L-2-phenylisopropyl)adenosine, the usual order of potency for activation of stimulatory adenosine receptors. Theophylline (100 microM), an adenosine receptor antagonist, reduced the short-circuit current response to adenosine and 2-chloroadenosine by 85-90%. Amiloride, an agent that inhibits both basal and adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated short-circuit current in A6 epithelia, completely and reversibly inhibited short-circuit current stimulated by 2-chloroadenosine. Adenosine and 2-chloroadenosine stimulated adenylate cyclase activity in a crude membrane preparation from A6 cells. Stimulation by adenosine was blocked by adenosine deaminase. 2-Chloroadenosine increased cell cAMP accumulation in intact epithelia. The results provide evidence that adenosine and adenosine receptor agonists stimulate adenylate cyclase and active sodium transport in an epithelial cell line of renal origin.

Novel therapeutics acting via purine receptors

“…Therefore, it seems reasonable to assume that adenosine-induced antidiuresis and antinatriuresis and, by inference, methylxanthine-induced diuresis and natriuresis, can be mediated by both renal hemodynamic and direct tubular mechanisms. Consistently, adenosine analogs stimulate active sodium transport in toad kidney cells [47]. Moreover, binding studies and studies of adenylate cyclase activity demonstrate the presence of both A 1 and A 2 -adenosine receptors [48].…”

Purinergic regulation of epithelial transport

“…With regard to epithelial transport in the kidney, it has been known that adenosine stimulates sodium transport since Lang et al (1985) first described it in Xenopus laevis renal epithelial A6 cells, a common model of the mammalian collecting duct. The net effect of adenosine stimulation is sodium transport from the lumenal to the serosal surface, making antagonists of these receptors possible candidates for diuretic therapy.…”

Adenosine Biosynthesis in the Collecting Duct

“…Several lines of evidence indicate that adenosine importantly regulates ion transport in collecting duct (CD) epithelial cells: 1) A 1 receptors are more highly expressed in CDs compared with other nephron segments (Smith et al, 2001); 2) in A6 cells, a model system for transport in the CD and in collecting ducts adenosine receptor agonists alter ion transport (Lang et al, 1985;Yagil, 1990;Schwiebert et al, 1992;Edwards and Spielman, 1994;Yagil et al, 1994;Ma and Ling, 1996;Hoenderop et al, 1998;Macala and Hayslett, 2002); and 3) administration of selective A 1 receptor antagonists increases sodium excretion without enhancing potassium excretion (Kuan et al, 1993), a pharmacological profile consistent with a diuretic action in CDs. Although endogenous adenosine significantly modulates transport in CDs, the sources of endogenous adenosine that mediate this effect are unknown.…”