Autor(es): Scott Brett N; Yu Ming-Jiun; Lee Lenora W; Beyenbach Klaus W

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

Palavras-Chave: Transepithelial Na+ secretion; Transepithelial K+ secretion; Transepithelial Cl- secretion; Barium block; K+ channel; Bumetanide; Na+/K+/2Cl- cotransport; Basolateral membrane voltage; Cell input resistance; Transepithelial voltage; Transepithelial resistance

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

Identificador do objeto digital: 10.1242/jeb.00932

Descritores: Aedes aegypti - Cell ; Aedes aegypti - Proteins

Data de publicação: 2004

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