Intracellular and luminal pH measurements of Malpighian tubules of the mosquito Aedes aegypti: the effects of cAMP

In order to understand the critical role that hydrogen ions play in fluid s ecretion in Malpighian tubules, intracellular and luminal pH and K+ measure ments were performed in isolated Malpighian tubules of the yellow fever mos quito (Aedes aegypti). The intracellular pH was 7.03+/-0.05 (n=15 Malpighia n tubules (MT)) and the luminal pH was 7.19+/-0.09 (n=99 MT) when bathed in saline at a pH of 7.0, The lumen potential is positive, thus net proton se cretion into the lumen is active. The intracellular and the luminal K+ conc entrations were 75+/-9 mM (n=15) and 102+/-13 mM (n=9 MT) respectively. Cyc lic AMP analogues accelerated fluid secretion and at the same time acidifie d the cell without affecting the luminal pH. Both effects were abolished by an isomer of adenosine-3',5' cyclic monophosphothioate (cAMPS), the Rp-cAM PS, known to inhibit protein kinase A. The results suggest that in the pres ence of cAMP the properties of the cation/H+ exchanger are affected and tha t this may be a result of phosphorylation of a Na+/2H+ antiporter located o n the apical membrane. (C) 1999 Elsevier Science Ltd. All rights reserved.