Mechanisms of K+ transport across basolateral membranes of principal cells in Malpighian tubules of the yellow fever mosquito,Aedes aegypti

Abstract

SUMMARY 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 Ba2+ (5 mmol l–1) significantly decreased transepithelial (TEP) fluid secretion (Vs) 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,Ba2+ had the following significant electrophysiological effects: it depolarized the TEP voltage (Vt) from 19.4 mV to 17.2 mV,increased the TEP resistance (Rt) from 6.4 kΩcm to 6.9 kΩcm, hyperpolarized the basolateral membrane voltage of principal cells (Vbl) from –75.2 mV to –88.2 mV and increased the cell input resistance from 363.7 kΩ to 516.3 kΩ. These effects of Ba2+ reflect the block of K+ channels that, apparently, are also permeable to Na+. Bumetanide (100μmol 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 Ba2+ completely inhibited TEP electrolyte and fluid secretion, with fast and slow kinetics reflecting the Ba2+ block of basolateral membrane K+channels and the inhibition of Na+/K+/2Cl– cotransport, respectively. The single and combined effects of Ba2+ 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+.

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

“…A similar Ba 2+ -sensitive K + conductance has been identified in other insects (Morgan and Mordue, 1983;O'Donnell and Maddrell, 1984;Baldrick et al, 1988;Leyssens et al, 1992;Neufeld and Leader, 1998;Wiehart et al, 2003;Ianowski and O'Donnell, 2004;Scott et al, 2004). There was no evidence of a significant Na + conductance, but a basolateral Cl -conductance was revealed after K + channels were blocked by Ba 2+ .…”

“…Bumetanide-sensitive Na + /K + /2Cl -cotransport has been demonstrated in the Malpighian tubules of R. prolixus and D. melanogaster (Ianowski et al, 2002;Ianowski and O'Donnell, 2004), and contributes to ion uptake in T. oceanicus (Xu and Marshall, 1999a;Marshall and Clode, 2009), A. aegypti (Hegarty et al, 1991;Scott et al, 2004), Manduca sexta (Audsley et al, 1993;Reagan, 1995), L. migratoria (Al-Fifi et al, 1998), Tenebrio molitor (Wiehart et al, 2003) and F. polyctena (Leyssens et al, 1994). A putative Na + /K + /2Cl -cotransporter has been cloned from the Malpighian tubules of M. sexta (Reagan, 1995), but mRNA encoding its homologue (CG31547) (Pullikuth et -cotransport is driven by the Na + electrochemical gradient ( bNa /F) across the basolateral membrane, which is maintained by active Na + extrusion into the lumen and bath.…”

Transport of H+, Na+ and K+ across the posterior midgut of blood-fed mosquitoes (Aedes aegypti)

“…Bumetanide is well-known as an inhibitor of basolateral Na + :K + :2Cl -cotransport in the Malpighian tubules of dipterans (Scott et al, 2004;Ianowski & O'Donnell, 2004) and other species (e.g. crickets; Coast, 2012).…”

X-ray microanalysis of Rb+ entry into cricket Malpighian tubule cellsviaputative K+ channels

“…Wiehart et al, 2003a;Ianowski and O'Donnell, 2004;Scott et al, 2004). The third possible mechanism for K + entry is via Ba 2+ sensitive K + channels (e.g.…”

“…The third possible mechanism for K + entry is via Ba 2+ sensitive K + channels (e.g. Leyssens et al, 1993;Leyssens et al, 1994;Wiehart et al, 2003b;Scott et al, 2004). The role of the latter in basolateral transport processes in vertebrate epithelia has been recently reviewed (Cotton, 2000;Warth, 2003).…”