Autor(es): Scott, B. N.; Yu, M. J.; Lee, L. W.; Beyenbach, K. W.

Resumo: The mechanisms of K super(+) entry from the hemolymph into principal cells of Malpighian tubules were investigated in the yellow fever mosquito, Aedes aegypti. The K super(+) channel blocker Ba super(2+) (5 mmol l super(-1)) significantly decreased transepithelial (TEP) fluid secretion (V sub(s)) from 0.84 nl min super(-1) to 0.37 nl min super(-1) and decreased the K super(+) concentration in secreted fluid from 119.0 mmol l super(-1) to 54.3 mmol l super(-1) with no change in the Cl super(-) concentration. Even though the Na super(+) concentration increased significantly from 116.8 mmol l super(-1) to 144.6 mmol l super(-1), rates of TEP ion secretion significantly decreased for all three ions. In addition, Ba super(2+) had the following significant electrophysiological effects: it depolarized the TEP voltage (V sub(t)) from 19.4 mV to 17.2 mV, increased the TEP resistance (R sub(t)) from 6.4 k Omega cm to 6.9 k Omega cm, hyperpolarized the basolateral membrane voltage of principal cells (V sub(bl)) from -75.2 mV to -88.2 mV and increased the cell input resistance from 363.7 k Omega to 516.3 k Omega . These effects of Ba super(2+) reflect the block of K super(+) channels that, apparently, are also permeable to Na super(+). Bumetanide (100 mu mol l super(-1)) had no effect on TEP fluid secretion and electrical resistance but significantly decreased TEP K super(+) secretion, consistent with the inhibition of electroneutral Na super(+)/K super(+)/2Cl super(-) cotransport. TEP Na super(+) secretion significantly increased because other Na super(+) entry pathways remained active. Bumetanide plus Ba super(2+) completely inhibited TEP electrolyte and fluid secretion, with fast and slow kinetics reflecting the Ba super(2+) block of basolateral membrane K super(+) channels and the inhibition of Na super(+)/K super(+)/2Cl super(-) cotransport, respectively. The single and combined effects of Ba super(2+) and bumetanide suggest that (1) K super(+) channels and Na super(+)/K super(+)/2Cl super(-) cotransport are the primary mechanisms for bringing K super(+) into cells, (2) K super(+) channels mediate a significant Na super(+) influx, (3) Na super(+) has as many as four entry pathways and (4) the mechanisms of TEP K super(+) and Na super(+) secretion are coupled such that complete block of TEP K super(+) renders the epithelium unable to secrete Na super(+).

Palavras-Chave: Sodium; Ions; Haemolymph; Secretion; Potassium; Epithelia; Electrophysiology; Aquatic insects; Hemolymph; Malpighian tubules; Epithelium; Aedes aegypti; Culicidae

Imprenta: Journal of Experimental Biology, v. 207, n. 10, p. 1655-1663, 2004.

Descritores: Aedes aegypti - Cell

Data de publicação: 2004

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