OUABAIN-INSENSITIVE NA-ATPASE ACTIVITY OF MALPIGHIAN TUBULES FROM RHODNIUS-PROLIXUS()

In the present paper, we show the existence of a furosemide-sensitive Na+-stimulated, Mg2+-dependent ATPase activity in cell lysates of Malp ighian tubular cells from Rhodnius prolixus, which could be the bioche mical expression of the Na+-pump. The main characteristics of this act ivity are: (1) K-0.5 for Na+ = 1.49 +/- 0.18 mM, (2) V-max = 2.8 +/- 0 .1 nmol inorganic orthophosphate (Pi).mg prot(-1).min(-1), (3) it is f ully abolished by 2 mM furosemide, (4) it is insensitive to ouabain co ncentrations up to 10(-2) M, (5) it is sensitive to the presence of va nadate in the incubation medium indicating it to be a P-type ATPase, a nd (6) it is stimulated by nanomolar concentrations of Ca2+ in the inc ubation medium. (C) 1998 Elsevier Science Inc. All rights reserved.