Nucleotide receptors regulate membrane ion transport in renal epithelial cells.
Regulation of plasma membrane ion transport by endogenous purinergic receptors was assessed in a distal renal (A6) cell line. Nucleotide analogues stimulated Na-K-Cl cotransport activity with relative potencies of ATP > UTP > ATP gamma S > 2-methylthio-ATP = alpha,beta-methylene ATP. Activation of nucleotide receptors with extracellular ATP and nucleotide analogues increased intracellular calcium concentration ([Ca2+]i) primarily by release of intracellular calcium stores, with relative potency of agonists similar to that seen for stimulation of Na-K-Cl cotransport. Neither the change in [Ca2+]i nor the stimulation of cotransport was abolished by the adenosine receptor antagonist 8-(4-[N-(2-aminoethyl)carbamoylmethoxy]-phenyl)-1,3-dipropylxanthi ne (XAC). In contrast to the adenosine A2 receptor agonist 5'-N-ethylcarboxamidoadenosine, nucleotide analogues had no discernible effect on cytosolic adenosine 3',5'-cyclic monophosphate levels or adenylyl cyclase activity. To address possible mechanisms for stimulation of Na-K-Cl cotransport by the nucleotide receptor, 125I efflux and patch-clamp studies were used to measure chloride secretion. ATP and ionomycin markedly enhanced 125I efflux and whole cell currents, consistent with activation of chloride conductance pathways. Diphenylamine-2-carboxylate, a chloride channel blocker, eliminated the effects of ionomycin, forskolin, adenosine, and ATP on Na-K-Cl cotransport. This study demonstrates that nucleotide receptors in this model of renal epithelium initiate distinct regulation of Na-K-Cl cotransport. Nucleotide receptors may effect their responses through primary activation of membrane chloride channels.
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
J P
JP
Middleton
A W
AW
Mangel
S
S
Basavappa
J G
JG
Fitz
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007477:Ions; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000502:physiology*; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D002712:Chlorides; D007477:Ions; D011983:Receptors, Purinergic; D028021:Sodium-Potassium-Chloride Symporters; D000242:Cyclic AMP; D002118:Calcium