Intracellular Na+, K+ and Cl− activities in Acheta domesticus Malpighian tubules and the response to a diuretic kinin neuropeptide

Abstract

SUMMARY 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 (Vb), 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 Ba2+-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 Ba2+, and a current carried by the passive outward movement of Cl− accounts for the hyperpolarization of Vb in response to Ba2+. 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 Vb. 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.

Mechanisms of calcium sequestration by isolated Malpighian tubules of the house cricket Acheta domesticus

“…Ca 2+ is moved from cell-to-lumen thermodynamically uphill by active Ca 2+ exporting pumps since both chemical (∼1000-fold) and electrical (V apical = +71 mV lumen-positive) gradients across apical membranes of A. domesticus tubules oppose Ca 2+ entry into the lumen (Coast, 2012). Plasma membrane Ca 2+ -ATPase (PMCA) pumps have been localized to the apical membranes in tubules of the gypsy moth, Lymantria dispar (Pannabecker, Smith, Beyenbach, & Wasserman, 1995).…”

“…It is well established that Malpighian tubules of insects (A. domesticus, Teleogryllus oceanicus, D. melanogaster, Rhodnius prolixus) secrete calcium into the primary urine, contributing to the elimination of excess dietary calcium (Maddrell et al, 1991;Marshall, Cooper, Rippon, & Patak, 1993;O'Donnell & Maddrell, 1995;Spring & Hazelton, 1987). Ca 2+ is moved from cell-to-lumen thermodynamically uphill by active Ca 2+ exporting pumps since both chemical (∼1000-fold) and electrical (V apical = +71 mV lumen-positive) gradients across apical membranes of A. domesticus tubules oppose Ca 2+ entry into the lumen (Coast, 2012). Plasma membrane Ca 2+ -ATPase (PMCA) pumps have been localized to the apical membranes in tubules of the gypsy moth, Lymantria dispar (Pannabecker, Smith, Beyenbach, & Wasserman, 1995).…”

The effect of cold acclimation on active ion transport in cricket ionoregulatory tissues

“…Transporters include the Na + -K + -2Clcotransporter (NKCC, which imports Na + , K + , and Clacross the basolateral cell membrane), carbonic anhydrase (CA, which provides cytosolic protons), and V-ATPase (which pumps protons to the lumen for future exchange with intracellular cations; Chintapalli et al, 2013;Coast, 2012;Halberg et al, 2015). Highly convoluted, mitochondria-dense paracellular channels in the rectal pads form the scalariform complex, in which membrane-bound Na + -K + ATPase (NKA) establishes a high extracellular [Na + ].…”

Comparative study of the protective effects of terfenadine and amiodarone on barium chloride/aconitine-induced ventricular arrhythmias in rats: A potential role of terfenadine

“…In the meantime, these two drugs demonstrated similar preventative and therapeutic effects on various arrhythmias triggered by BaCl 2 or aconitine. It is well established that infusion of BaCl 2 leads to delayed afterdepolarization and triggered activity through increases in Na + and Ca 2+ inflow to the myocardium, promoting the genesis of arrhythmia (25,26). Most importantly, electrophysiological studies have found that Ba 2+ was the potential blocker of various K + channels and permeation of Ba 2+ through the K + channel may impede the presence of K + in the external solution, which may result in the increase of autorhythmicity of the myocardium to produce ventricular arrhythmia (27)(28)(29).…”