Electrochemical gradients across Malpighian tubules of the house cricket, Acheta domesticus, and the mode of action of kinin and CRF-related diuretics

Double-barrelled ion-selective microelectrodes were used to measure Na+, K+ and Clactivities in the principal cells of cricket Malpighian tubules, allowing electrochemical gradients across apical and basal membranes to be calculated. At the basal membrane, K+ and Clgradients support passive exit into the bathing medium. A thermodynamic analysis shows both ions can be taken up by Na+/K+/2Clcotransport driven by a favourable Na+ gradient. At the apical membrane, cations are actively transported into the lumen whereas Clmoves passively. Evidence is presented to show that diuretic kinins open an apical membrane Clconductance whereas Achdo-DH acts via cAMP to stimulate the basal membrane NKCC.