title: Activation of Na+/H+ exchange by protein phosphatase inhibitors in red blood cells of the frog Rana ridibunda.
abstract: The present study was designed to evaluate the role of protein phosphatases in regulation of sodium transport in the marsh frog erythrocytes using 22Na as a tracer. For this purpose the cells were treated with several known inhibitors of protein phosphatases. In standard isotonic medium, exposure of the cells to 10 mmol l(-1) NaF, 20 nmol l(-1) calyculin A or 0.1 mmol l(-1) cantharidin resulted in a significant (1.7-fold) increase in unidirectional ouabain-insensitive Na+ influx. The Na+ influx in frog red cells was progressively activated as the medium osmolality was increased by addition of 100, 200 or 300 mmol l(-1) sucrose to standard isotonic medium. The stimulatory effect of protein phosphatase blockers on Na+ influx was much higher in hypertonic medium containing 100 or 200 mmol l(-1) sucrose than that in isotonic medium. Stimulation of Na+ transport enhanced with increasing concentrations of calyculin A, and half-maximal activation (EC50) was obtained at 16 nmol l(-1). However, Na+ influx induced by strong hypertonic treatment (+300 mmol l(-1) sucrose) was not altered further in the presence of protein phosphatase inhibitors. The changes in Na+ influx evoked by protein phosphatase inhibitors and hypertonic treatment were associated with a rise in the intracellular Na+, but not K+, content. Enhancement in Na+ influx after addition of protein phosphatase blockers to cell suspension in isotonic or hypertonic media was almost completely inhibited by Na+/H+ exchange inhibitors, amiloride and ethyl-isopropyl-amiloride. The basal Na+ influx in frog erythrocytes in isotonic medium was relatively low (1.7 mmol/l cells/h) and not affected by 1 mmol l(-1) amiloride. Thus, the data obtained clearly indicate that Na+/H+ exchanger in the marsh frog red blood cells is under tight regulatory control, in all likelihood via protein phosphatases of types PP-1 and PP-2A.
authors.affiliation: Laboratory of Comparative Biochemistry of Inorganic ions, Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, Thorez pr. 44, 194223, St. Petersburg, Russia. gusev@iephb.ru
authors.forename: G P
authors.initials: GP
authors.lastname: Gusev
authors.forename: T I
authors.initials: TI
authors.lastname: Ivanova
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002193:Cantharidin; D004912:Erythrocytes / Q000201:enzymology*; D008387:Marine Toxins; D010080:Oxazoles; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D011895:Rana ridibunda / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D012969:Sodium Fluoride; D012979:Sodium Radioisotopes
chemical_list: D008387:Marine Toxins; D010080:Oxazoles; D012979:Sodium Radioisotopes; C059041:calyculin A; D012969:Sodium Fluoride; D012964:Sodium; D010749:Phosphoprotein Phosphatases; D002193:Cantharidin