KCL REABSORPTION BY THE LOWER MALPIGHIAN TUBULE OF RHODNIUS-PROLIXUS - INHIBITION BY CL- CHANNEL BLOCKERS AND ACETAZOLAMIDE

Iono- and osmoregulation by the blood-feeding hemipteran Rhodnius prol ixus involves coordinated actions of the upper and lower Malpighian tu bules. The upper tubule secretes ions (Na+, K+, Cl-) and water, wherea s the lower tubule reabsorbs K+ and Cl- but not water, The extent of K Cl reabsorption by the lower tubule in vitro was monitored by ion-sele ctive microelectrode measurement of Cl- and/or K+ concentration in dro plets of fluid secreted by Malpighian tubules isolated under oil. An e arlier study proposed that K+ reabsorption involves an omeprazole-sens itive apical K+/H+ ATPase and Ba2+-sensitive basolateral K+ channels, This paper examines the effects acetazolamide and of compounds that in hibit chloride channels, Cl-/HCO3- exchangers and Na+/K+/2Cl(-) or K+/ Cl- co-transporters. The results suggest that Cl- reabsorption is inhi bited by acetazolamide and by Cl- channel blockers, including diphenyl amine-2-carboxylate(DPC) and 5-nitro-2-(3-phenylpropylamino) benzoic a cid (NPPB), but not by compounds that block Na+/K+/Cl- and K+/Cl- co-t ransporters. Measurements of transepithelial potential and basolateral membrane potential during changes in bathing saline chloride concentr ation indicate the presence of DPC-and NPPB-sensitive chloride channel s in the basolateral membrane, A working hypothesis of ion movements d uring KCl reabsorption proposes that Cl- moves from lumen to cell thro ugh a stilbene-insensitive Cl-/HCO3- exchanger and then exits the cell through basolateral Cl- channels. (C) 1997 Elsevier Science Ltd.