Stimulation of alpha 2-adrenergic receptors increases Na(+)-K(+)-ATPase activity in distal convoluted tubule cells.
The influence of alpha-adrenoceptor subtypes on Na+ transport in distal convoluted tubules (DCT) has not been examined due to the difficulty of isolating and quantifying responses in this segment. These experiments were designed to test the hypothesis that alpha-adrenergic receptors stimulate Na+ absorption in DCT cells. Norepinephrine and epinephrine increased 22Na+ uptake into immortalized mouse DCT cells by 49 and 55% compared with basal uptake. Selective alpha 2-agonists (guanabenz, clonidine, and B-HT 933) stimulated 22Na+ uptake by 39-45%, but alpha 1-agonists had no effect. alpha 2-Agonist-stimulated 22Na+ uptake was abolished with alpha 2-antagonists (yohimbine, idazoxan). The entry pathways for alpha 2-agonist-stimulated 22Na+ uptake were determined with the NaCl cotransport inhibitor, chlorothiazide (10(-4) M), and the Na+ channel blocker, amiloride (10(-6) M). Agonist-stimulated 22Na+ uptake was inhibited 42 +/- 5 with chlorothiazide and 47 +/- 7% with amiloride. These results suggested that alpha 2-receptors may activate Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase), resulting in an increased driving force for luminal Na+ entry through both pathways. Ouabain-suppressible 86Rb uptake and intracellular Na+ activity ([Na+]i; measured in single cells on glass cover slips loaded with the fluorescent probe sodium-binding benzofuran isophthalate) were used to measure Na(+)-K(+)-ATPase activity. alpha 2-Agonists significantly increased 86Rb uptake within 30 s. After 2.5 min, epinephrine and B-HT 933 decreased [Na+]i from a control level of 13 +/- 1 to 5 +/- 1 mM.(ABSTRACT TRUNCATED AT 250 WORDS)
Gesek
F A
FA
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755.
D000818:Animals; D002461:Cell Line, Transformed; D007425:Intracellular Membranes / Q000378:metabolism; D007686:Kidney Tubules, Distal / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D011942:Receptors, Adrenergic, alpha; D012964:Sodium; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium