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Contributions of K+:Cl- cotransport and Na+/K+-ATPase to basolateral ion transport in malpighian tubules of Drosophila melanogaster.
J Exp Biol. 1999 Jun; 202(Pt 11):1561-70.JE

Abstract

Mechanisms of Na+ and K+ transport across the basolateral membrane of isolated Malpighian tubules of Drosophila melanogaster were studied by examining the effects of ion substitution and putative inhibitors of specific ion transporters on fluid secretion rates, basolateral membrane potential and secreted fluid cation composition. Inhibition of fluid secretion by [(dihydroindenyl)oxy]alkanoic acid (DIOA) and bumetanide (10(-)4 mol l-1) suggested that a K+:Cl- cotransporter is the main route for K+ entry into the principal cells of the tubules. Differences in the effects of bumetanide on fluxes of K+ and Na+ are inconsistent with effects upon a basolateral Na+:K+:2Cl- cotransporter. Large differences in electrical potential across apical (>100 mV, lumen positive) and basolateral (<60 mV, cell negative) cell membranes suggest that a favourable electrochemical gradient for Cl- entry into the cell may be used to drive K+ into the cell against its electrochemical gradient, via a DIOA-sensitive K+:Cl- cotransporter. A Na+/K+-ATPase was also present in the basolateral membrane of the Malpighian tubules. Addition of 10(-)5 to 10(-)3 mol l-1 ouabain to unstimulated tubules depolarized the basolateral potential, increased the Na+ concentration of the secreted fluid by 50-73 % and increased the fluid secretion rate by 10-19 %, consistent with an increased availability of intracellular Na+. We suggest that an apical vacuolar-type H+-ATPase and a basolateral Na+/K+-ATPase are both stimulated by cyclic AMP. In cyclic-AMP-stimulated tubules, K+ entry is stimulated by the increase in the apical membrane potential, which drives K+:Cl- cotransport at a faster rate, and by the stimulation of the Na+/K+-ATPase. Fluid secretion by cyclic-AMP-stimulated tubules was reduced by 26 % in the presence of ouabain, suggesting that the Na+/K+-ATPase plays a minor role in K+ entry into the tubule cells. Malpighian tubules secreted a Na+-rich (150 mmol l-1) fluid at high rates when bathed in K+-free amino-acid-replete saline (AARS). Secretion in K+-free AARS was inhibited by amiloride and bafilomycin A1, but not by bumetanide or hydrochlorothiazide, which inhibit Na+:Cl- cotransport. There was no evidence for a Na+ conductance in the basolateral membrane of unstimulated or cyclic-AMP-stimulated tubules. Possible mechanisms of Na+ entry into the tubule cells include cotransport with organic solutes such as amino acids and glucose.

Authors+Show Affiliations

Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1. lintons@mcmail.cis.mcmaster.caNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

10229702

Citation

Linton, S M., and M J. O'Donnell. "Contributions of K+:Cl- Cotransport and Na+/K+-ATPase to Basolateral Ion Transport in Malpighian Tubules of Drosophila Melanogaster." The Journal of Experimental Biology, vol. 202, no. Pt 11, 1999, pp. 1561-70.
Linton SM, O'Donnell MJ. Contributions of K+:Cl- cotransport and Na+/K+-ATPase to basolateral ion transport in malpighian tubules of Drosophila melanogaster. J Exp Biol. 1999;202(Pt 11):1561-70.
Linton, S. M., & O'Donnell, M. J. (1999). Contributions of K+:Cl- cotransport and Na+/K+-ATPase to basolateral ion transport in malpighian tubules of Drosophila melanogaster. The Journal of Experimental Biology, 202(Pt 11), 1561-70.
Linton SM, O'Donnell MJ. Contributions of K+:Cl- Cotransport and Na+/K+-ATPase to Basolateral Ion Transport in Malpighian Tubules of Drosophila Melanogaster. J Exp Biol. 1999;202(Pt 11):1561-70. PubMed PMID: 10229702.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Contributions of K+:Cl- cotransport and Na+/K+-ATPase to basolateral ion transport in malpighian tubules of Drosophila melanogaster. AU - Linton,S M, AU - O'Donnell,M J, PY - 1999/5/7/pubmed PY - 1999/5/7/medline PY - 1999/5/7/entrez SP - 1561 EP - 70 JF - The Journal of experimental biology JO - J Exp Biol VL - 202 IS - Pt 11 N2 - Mechanisms of Na+ and K+ transport across the basolateral membrane of isolated Malpighian tubules of Drosophila melanogaster were studied by examining the effects of ion substitution and putative inhibitors of specific ion transporters on fluid secretion rates, basolateral membrane potential and secreted fluid cation composition. Inhibition of fluid secretion by [(dihydroindenyl)oxy]alkanoic acid (DIOA) and bumetanide (10(-)4 mol l-1) suggested that a K+:Cl- cotransporter is the main route for K+ entry into the principal cells of the tubules. Differences in the effects of bumetanide on fluxes of K+ and Na+ are inconsistent with effects upon a basolateral Na+:K+:2Cl- cotransporter. Large differences in electrical potential across apical (>100 mV, lumen positive) and basolateral (<60 mV, cell negative) cell membranes suggest that a favourable electrochemical gradient for Cl- entry into the cell may be used to drive K+ into the cell against its electrochemical gradient, via a DIOA-sensitive K+:Cl- cotransporter. A Na+/K+-ATPase was also present in the basolateral membrane of the Malpighian tubules. Addition of 10(-)5 to 10(-)3 mol l-1 ouabain to unstimulated tubules depolarized the basolateral potential, increased the Na+ concentration of the secreted fluid by 50-73 % and increased the fluid secretion rate by 10-19 %, consistent with an increased availability of intracellular Na+. We suggest that an apical vacuolar-type H+-ATPase and a basolateral Na+/K+-ATPase are both stimulated by cyclic AMP. In cyclic-AMP-stimulated tubules, K+ entry is stimulated by the increase in the apical membrane potential, which drives K+:Cl- cotransport at a faster rate, and by the stimulation of the Na+/K+-ATPase. Fluid secretion by cyclic-AMP-stimulated tubules was reduced by 26 % in the presence of ouabain, suggesting that the Na+/K+-ATPase plays a minor role in K+ entry into the tubule cells. Malpighian tubules secreted a Na+-rich (150 mmol l-1) fluid at high rates when bathed in K+-free amino-acid-replete saline (AARS). Secretion in K+-free AARS was inhibited by amiloride and bafilomycin A1, but not by bumetanide or hydrochlorothiazide, which inhibit Na+:Cl- cotransport. There was no evidence for a Na+ conductance in the basolateral membrane of unstimulated or cyclic-AMP-stimulated tubules. Possible mechanisms of Na+ entry into the tubule cells include cotransport with organic solutes such as amino acids and glucose. SN - 0022-0949 UR - https://www.unboundmedicine.com/medline/citation/10229702/Contributions_of_K+:Cl__cotransport_and_Na+/K+_ATPase_to_basolateral_ion_transport_in_malpighian_tubules_of_Drosophila_melanogaster_ L2 - http://jeb.biologists.org/cgi/pmidlookup?view=long&amp;pmid=10229702 DB - PRIME DP - Unbound Medicine ER -