Activation of the Na+-K+ pump by hyposmolality through tyrosine kinase-dependent Cl- conductance in Xenopus renal epithelial A6 cells

1. We studied the regulatory mechanism of Na+ transport by hyposmolality in renal epithelial A6 cells. 2. Hyposmolality increased (1) Na+ absorption, which was detected as an amiloride-sensitive short-circuit current (I-Na), (2) Na+-K+ pump activity, (3) basolateral Cl- conductance (G(b,Cl)), and (4) phosphorylation of tyrosine, suggesting an increase in activity of protein tyrosine kinase (PTK). 3. A Cl- channel blocker, 5-nitro-2-(3-phenylpropylamino) -benzoate (NPPB), which abolished G(b,Cl), blocked the I-Na by inhibiting the Na+-K+ pump without any direct effect on amiloride-sensitive Na+ channels. Diminution of G(b,Cl) by Cl- replacement with a less permeable anion, gluconate, also decreased the hyposmolality-increased Na+-K+ pump activity. 4. The PTK inhibitors tyrphostin A23 and genistein induced diminution of the hyposmolality-stimulated C-b,C-Cl, which was associated with attenuation of the hyposmolality-increased Na+-K+ pump activity. 5. Taken together, these observations suggest that: (1) hyposmolality activates PTK(; (2) the activated PTK increases G(b,Cl); and (3) the PTK-increased G(b,Cl) stimulates the Na+-K+ pump. 6. This PTK-activated G(b,Cl)-mediated signalling of hyposmolality is a novel pathway for stimulation of the Na+-K+ pump.