Osmotic Modulation of the Ouabain-Sensitive (Na++K+)ATPase from Malpighian Tubules of Rhodnius prolixus

• Published in: Zeitschrift für Naturforschung C. A journal of biosciences Vol. 53; no. 9; pp. 911 - 917
• Main Authors: Caruso-Neves, C., Meyer-Fernandes, J. R., Lopes, A. G.
• Format: Journal Article
• Language: English
• Published: Verlag der Zeitschrift für Naturforschung 01.10.1998
• Subjects: (Na++K+)ATPase; Cell Volume Regulation; Malpighian Tubule; Na+-ATPase; Osmotic Modulation; Rhodnius; Sphingosine
• ISSN: 0939-5075; 1865-7125
• DOI: 10.1515/znc-1998-9-1021

The presence and regulation by hyperosmotic medium of the ouabain-sensitive (Na +K )ATPase of the Malpighian tubule cells of Rhodnius prolixus was investigated. The ouabain-sensitive (Na +K )ATPase activity was 5.4 ± 0.5 nmol Pi x mg x min . Vanadate 100 μM completely abolished this ATPase activity. In hyperosmotic medium, obtained by addition of 180 mᴍ mannitol, the (Na +K )ATPase activity was inhibited by 60%. When the cell lysates were preincubated in hyperosmotic medium for 30 minutes and the ATPase activity was assayed in isosmotic medium, the (Na +K )ATPase activity was not modified. Addition of 50 ng/ml sphingosine, a protein kinase C inhibitor, abolished the inhibition of (Na +K )ATPase activity in hyperosmotic medium. Furtherm ore, phorbol ester (TPA), an activator of protein kinase C, mimicked the effect of hyperosmotic shock on (Na +K )ATPase activity. The increase in Ca concentration decreased the (Na +K )ATPase activity by 60% in isosmotic medium, with maximal effect obtained in 10 m Ca . No effect was observed in hyperosmotic medium. The inhibitory effect of Ca on the (Na +K )ATPase was not reversed by sphingosine. These results indicate that the ouabain-sensitive (Na +K ) ATPase activity of the Malpighian tubule is regulated by both increasing Ca concentration and by the osmolality of the medium by different and integrative ways.