title: Intracellular Na+, K+ and Cl- activities in Acheta domesticus Malpighian tubules and the response to a diuretic kinin neuropeptide.
abstract: The mechanism of primary urine production and the activity of a diuretic kinin, Achdo-KII, were investigated in malpighian tubules of Acheta domesticus by measuring intracellular Na(+), K(+) and Cl(-) activities, basolateral membrane voltage (V(b)), fluid secretion and transepithelial ion transport. Calculated electrochemical gradients for K(+) and Cl(-) across the basolateral membrane show they are actively transported into principal cells, and basolateral Ba(2+)-sensitive K(+) channels do not contribute to net transepithelial K(+) transport and fluid secretion. A basolateral Cl(-) conductance was revealed after the blockade of K(+) channels with Ba(2+), and a current carried by the passive outward movement of Cl(-) accounts for the hyperpolarization of V(b) in response to Ba(2+). Ion uptake via Na(+)/K(+)/2Cl(-) cotransport, driven by the inwardly directed Na(+) electrochemical gradient, is thermodynamically feasible, and is consistent with the actions of bumetanide, which reduces fluid secretion and both Na(+) and K(+) transport. The Na(+) gradient is maintained by its extrusion across the apical membrane and by a basolateral ouabain-sensitive Na(+)/K(+)-ATPase. Achdo-KII has no significant effect on the intracellular ion activities or V(b). Electrochemical gradients across the apical membrane were estimated from previously published values for the levels of Na(+), K(+) and Cl(-) in the secreted fluid. The electrochemical gradient for Cl(-) favours passive movement into the lumen, but falls towards zero after stimulation by Achdo-KII. This coincides with a twofold increase in Cl(-) transport, which is attributed to the opening of an apical Cl(-) conductance, which depolarises the apical membrane voltage.
authors: Birkbeck, University of London, London WC1E 7HX, UK. g.coast@bbk.ac.uk
authors: Geoffrey M
authors: GM
authors: Coast
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D001826:Body Fluids / Q000187:drug effects; D002138:Calibration; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D004553:Electric Conductivity; D055724:Electrophysiological Phenomena / Q000187:drug effects; D005260:Female; D006135:Gryllidae / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D017736:Ion-Selective Electrodes; D007477:Ions; D007705:Kinins / Q000494:pharmacology*; D008317:Malpighian Tubules / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride
chemical_list: D002712:Chlorides; D004232:Diuretics; D007477:Ions; D007705:Kinins; D009479:Neuropeptides; D001464:Barium; D012965:Sodium Chloride; D012964:Sodium; D011188:Potassium