Excretion

Excretion in the House cricket, Acheta Domesticus: Effects of secretagogues on malpighian tubule electrophysiology and secretion rate

J.H. Spring 1 , M.J. O’Donnell 2 & S.R. Hazelton 1

1 Dept. Biology, Univ. of Louisiana at Lafayette, Lafayette, LA 70504-2451, USA; 2 Dept. Biology, McMaster Univ., 1280 Main St. West, Hamilton, Ont., Canada L8S 4K1Ad

The Malpighian tubules of A. domesticus are comprised of three regions, distal, mid and proximal, each consisting of a single cell type. The mid-tubule is the largest segment (?75% of the total length) and its secretory activity is controlled by a suite of neuropeptides. Basolateral membrane (Vbl) and transepithelial potentials (TEP) were determined using microelectrodes, while secretion rates were measured using Ramsay-type preparations. Altering the concentrations of specific ions in the bathing saline suggests that the basal membrane is predominantly permeable to K + , which provides about 70% of Vbl. Dibutyryl cAMP (1 mM) and Manduca sexta diuretic peptide 1 (Mas-DP1; 5 nM) both acted to increase TEP but not Vbl, indicating that they act on the apical membrane. We had previously suggested that cAMP and the diuretic peptides might act by increasing the permeability of the basolateral membrane to Na + , however, these data and the reduction in secretion rate by bumetanide (0.1 mM) indicated that basolateral Na + entry is restricted to the Na:K:2 Cl cotransporter. Whether cAMP and Mas-DP1 act to stimulate the apical V-ATPase, as is the case in Drosophila, or the Na + /H + and K + /H + antiporters, as is the case in Aedes, has not been determined. The myokinins, achetakinin 1 and 2 (AK-1, AK-2; 5 nM) decreased TEP by up to 73% without affecting Vbl. The chloride channel blocker NPPB reduced the effect of AK-1 on TEP by 75%, indicating that these peptides also act on the apical membrane and not via a paracellular pathway. It appears that the kinins act at quite different sites in different species, e.g. on the stellate cells in Drosophila, on a paracellular pathway in Aedes, and possibly on apical ion channels in A.domesticus. Supported by NSF grant IBN-9807948 to JHS.

Index terms: diuretic peptide, achetakinin, cAMP

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