Purinergic-mediated inhibition of Na+-K+-ATPase in proximal tubule cells: elevated cytosolic Ca2+ is not required.
The involvement of cytosolic Ca2+ concentration ([Ca2+]i) as messenger for the regulation of Na+-K+-ATPase activity was investigated in a renal cell line recently developed by immortalization of early proximal tubule primary cultures from the Wistar-Kyoto rat strain. Na+-K+-ATPase was measured as short-circuit current (Isc) in intact monolayers after permeabilization of the apical plasma membrane with amphotericin B. With symmetrical solutions, Isc quantitatively reflects Na+-K+-ATPase activity as judged by ouabain inhibition and dependence on Na+ and K+. Extracellular ATP (50% effective concentration = 0.32 mM) on the apical side produced acute inhibition of Na+-K+-ATPase-generated Isc of up to 50%. The inhibition peaked within 1 min and lasted approximately 5 min. The potency order was ATP > ADP >> beta,gamma-methyleneadenosine 5'-triphosphate = UTP, consistent with a P2y receptor. Extracellular ATP also stimulated a transient increase in [Ca2+]i. This increase had a similar time course as the inhibition of ATPase and reached a peak change of approximately 120 nM. However, the elevation of [Ca2+]i is not required in the purinergic inhibition of the Na+-K+-ATPase, since, first, increases in [Ca2+]i produced with a Ca2+ ionophore (ionomycin) failed to mimic the purinergic inhibition and, second, 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, which abolished the [Ca2+]i elevation, failed to block the purinergic inhibition.
Jin
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Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA.
Hopfer
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity; D005110:Extracellular Space / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D011921:Rats, Inbred WKY; D011983:Receptors, Purinergic / Q000502:physiology*; D015290:Second Messenger Systems; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D011983:Receptors, Purinergic; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium