Influence of Na+ intake on dopamine-induced inhibition of renal cortical Na(+)-K(+)-ATPase.
The enzyme L-amino acid decarboxylase (L-AADC), found in abundance in rat proximal tubule cell cytosol, converts L-dopa to dopamine. Dopamine, in turn, suppresses proximal tubule sodium transport by inhibiting Na(+)-K(+)-ATPase activity. We sought to determine whether changes in dietary sodium intake in rats lead to adaptation of dopamine formation and dopamine-induced Na(+)-K(+)-ATPase inhibition. In rats on a high-salt (HS) diet, the maximal velocity (Vmax) of renal cortical L-AADC was 78 +/- 19% higher than that in rats on a low-salt (LS) diet. The Michaelis constant (Km) of the enzyme remained unchanged. In renal cortical tubule cell suspensions the L-dopa-induced inhibition of ouabain-sensitive oxygen consumption (QO2) was significantly greater in rats on HS diet than in rats on LS diet. Furthermore, L-dopa completely inhibited the nystatin-induced rise in QO2 in the HS but not in the LS group. Carbidopa, an inhibitor of L-AADC, abolished the L-dopa-induced inhibition of nystatin-stimulated QO2 in cells from HS rats and was without significant effect in cells from LS rats. L-Dopa-stimulated K+ efflux was greater in cells from HS rats at 28 +/- 1 nmol.min-1.mg protein-1, compared with 7 +/- 6 nmol.min-1.ng protein-1 in cells from LS rats. By contrast, ouabain-stimulated K+ efflux did not differ between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Seri
I
I
Renal Division, Brigham and Women's Hospital, Boston, Massachusetts.
Kone
B C
BC
Gullans
S R
SR
Aperia
A
A
Brenner
B M
BM
Ballermann
B J
BJ
D000818:Animals; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000378:metabolism; D004032:Diet; D004039:Diet, Sodium-Restricted; D004298:Dopamine / Q000494:pharmacology*; D007672:Kidney Cortex / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000008:administration & dosage* / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D012964:Sodium; D001142:Aromatic-L-Amino-Acid Decarboxylases; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D004298:Dopamine