Ww. Jin et U. Hopfer, PURINERGIC-MEDIATED INHIBITION OF NA-K+-ATPASE IN PROXIMAL TUBULE CELLS - ELEVATED CYTOSOLIC CA2+ IS NOT REQUIRED(), American journal of physiology. Cell physiology, 41(4), 1997, pp. 1169-1177
The involvement of cytosolic Ca2+ concentration ([Ca2+](i)) as messeng
er for the regulation of Na+-K+-ATPase activity was investigated in a
renal cell line recently developed by immortalization of early proxima
l tubule primary cultures from the Wistar-Kyoto rat strain. Na+-K+-ATP
ase was measured as short-circuit current (I-sc) in intact monolayers
after permeabilization of the apical plasma membrane with amphotericin
B. With symmetrical solutions, I-sc quantitatively reflects Na+-K+-AT
Pase activity as judged by ouabain inhibition and dependence on Na+ an
d K+. Extracellular ATP (50%) effective concentration = 0.32 mM) on th
e apical side produced acute inhibition of Na+-K+-ATPase-generated I-s
c of up to 50%. The inhibition peaked within 1 min and lasted similar
to 5 min. The potency order was ATP > ADP >> beta,gamma-methyleneadeno
sine 5'-triphosphate UTP, consistent with a P-2y receptor. Extracellul
ar ATP also stimulated a transient increase in [Ca2+](i). This increas
e had a similar time course as the inhibition of ATPase and reached a
peak change of similar to 120 nM. However, the elevation of [Ca2+](i)
is not required in the purinergic inhibition of the Na+-K+-ATPase, sin
ce, first, increases in [Ca2+](i) produced with a Ca2+ ionophore (iono
mycin) failed to mimic the purinergic inhibition and, second, ,2-bis(2
-aminophenoxy)ethane=N,N,N',N'-tetraacetic acid, which abolished the [
Ca2+](i) elevation, failed to block the purinergic inhibition.