Na+/H+ exchanger activity and dopamine D1-Like receptor function in two opossum kidney cell clonal sublines

Background/Aims: The enhanced renal reabsorption of Na+ in hypertension is accompanied by a defective transduction of the renal dopamine D-1 receptor signal. The present study evaluated the response of the Na+/ H+ exchanger to dopamine D-1-like receptor stimulation in two clonal subpopulations of opossum kidney (OK) cells (OKLC and OKHC that are functionally different with respect to their ability to transport Na+.Methods: Na+/H+ exchanger activity was assayed as the initial rate of intracellular pH (pH) recovery after an acid load. The presence of D-1-like receptors was measured in saturation experiments with [H-3]-Sch 23390 in cell membranes. Results: V-max, values (in pH units/s) for Na+-dependent pH(i) recovery in OKHC cells (0.00521 +/- 0.0004) were twice those in OKHC (0.00202 +/- 0.0001), with similar K-m values.The selective D-1-like receptor agonist SKF 38393 (30 to 3000 nM) attenuated the Na+/H+ exchanger activity in OKHC cells more potently than in OKLC cells. GTPgammaS and forskolin were equipotent in inhibiting the Na+/H+ exchanger in OKHC cells and OKLC cells.The SKF 38393-induced increase in cyclic AMP levels in OKHC cells was greater than in OKLC cells. B-max values for the binding of [H-3]-Sch 23390 in OKHC cells were twice that in OKLC cells, with similar K-D values. The abundance of G(s)alpha protein in cell membranes of OKHC cells was similar to that in OKLC cells. Conclusion: The enhanced sensitivity of the Na+/H+ exchanger to inhibition by the D-1-Iike receptor agonist in OKHC cells correlated positively with the high density of D-1-like binding sites and the enhanced production of cyclic AMP during D-1-like receptor stimulation in OKHC cells. Copyright (C) 2002 S. Karger AG, Basel.