DOES DOPAMINE USE SEVERAL SIGNAL PATHWAYS TO INHIBIT NA-P-I TRANSPORTIN OK CELLS

In opossum kidney (OK) cells, L-dihydroxyphenylalanine (10 mu M) raise d dopamine to 10 nM and inhibited Na-inorganic phosphate (P-i) uptake 20% (P = 0.001). Inhibition was completely blocked by carbidopa or SCH 23390. Dopamine (1 mu M) inhibited uptake 55% (half-maximal inhibition , 0.03 mu M). Fenoldopam (0.1 mu M, DA(I) agonist) inhibited uptake 45 +/- 2%. DA, antagonists (SKF83566 and SCH23390), but not DA(2)-antago nist (sulpiride), blocked dopamine inhibition. Quinpirole (DA(2) agoni st) did not modify P-i uptake. Bisin-dolylmaleimide (10 mu M), a prote in kinase C inhibitor, blocked inhibition of P-i uptake by phorbol est er but had no effect on the response to dopamine. Dopamine inhibited P -i uptake in cells that had been exposed to phorbol ester for 18 to 24 h. Dopamine inhibition was not reduced by 1 mu M U73,122 but was redu ced 20% by 10 mu M, which is 10 times the concentration reported to co mpletely inhibit phospholipase C in OK cells.