title: A blood plasma inhibitor is responsible for circadian changes in rat renal Na,K-ATPase activity.
abstract: Rhythmic changes in activity following a circadian schedule have been described for several enzymes. The possibility of circadian changes in Na,K-ATPase activity was studied in homogenates of rat kidney cortex cells. Male Sprague-Dawley rats were kept on a schedule of 12h light (06:00-18:00 h) and 12 h darkness (18:00-06:00 h) for 2 weeks. At the end of the conditioning period, one rat was killed every 2 h, until completion of a 24 h cycle. Outermost kidney cortex slices were prepared, homogenized and assayed for Na,K-ATPase activity. The whole procedure was repeated six times. Na,K-ATPase activity shows an important oscillation (2 cycles/24 h). Peak activities were detected at 09:00 and 21:00 h, whereas the lowest activities were detected at 15:00 and 01:00-03:00 h. The highest activity was 40+/-3 nmoles Pi mg protein(-1)min(-1) (09:00 h), and the lowest was 79+/-3 nmoles Pi mg protein(-1)min(-1) (15:00 h). The amount of the Na+-stimulated phosphorylated intermediate is the same for the 09:00 h and 15:00 h homogenates. Preincubation of 09:00 h kidney cortex homogenates with blood plasma drawn from rats at either 03:00 h or 15:00 h, significantly inhibited their Na,K-ATPase activity. This inhibition was not seen when the preincubation was carried out with either 09:00 h or 21:00 h blood plasma. The striking oscillation (2 cycles/24 h) of the Na,K-ATPase activity of rat kidney cortex cells is ascribed to the presence of an endogenous inhibitor in blood plasma.
authors.affiliation: Laboratorio de Bioenergética Celular, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas (IVIC), A.P. 21827, Caracas 1020A, Venezuela.
authors.forename: Darío
authors.initials: D
authors.lastname: Segura
authors.forename: Antonio
authors.initials: A
authors.lastname: Eblen-Zajjur
authors.forename: Fulgencio
authors.initials: F
authors.lastname: Proverbio
authors.forename: Teresa
authors.initials: T
authors.lastname: Proverbio
authors.forename: Francisco
authors.initials: F
authors.lastname: Carrera
authors.forename: Celso
authors.initials: C
authors.lastname: Caruso-Neves
authors.forename: Reinaldo
authors.initials: R
authors.lastname: Marín
mesh_terms: D000818:Animals; D001685:Biological Factors / Q000302:isolation & purification / Q000494:pharmacology*; D002940:Circadian Rhythm / Q000502:physiology* / Q000528:radiation effects; D007672:Kidney Cortex / Q000201:enzymology* / Q000528:radiation effects; D008297:Male; D010766:Phosphorylation; D010949:Plasma / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012967:Sodium Dodecyl Sulfate; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism*
chemical_list: D001685:Biological Factors; D012967:Sodium Dodecyl Sulfate; D000254:Sodium-Potassium-Exchanging ATPase