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Na+ competes with K+ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus.
J Exp Biol. 2004 Oct; 207(Pt 21):3707-16.JE

Abstract

We examined the effects of bathing saline Na+/K+ ratio, bumetanide and hydrochlorothiazide on fluid and ion transport by serotonin-stimulated Malpighian tubules of Rhodnius prolixus. Previous pharmacological and electrophysiological studies indicate that a bumetanide-sensitive Na+/K+/2Cl- cotransporter is the primary route for basolateral ion entry into the cell during fluid secretion. The goal of this study was to resolve the apparent conflict between relatively high secretion rates by tubules bathed in K+-free saline and the evidence that Na+/K+/2Cl- cotransporters described in other systems have an absolute requirement for all three ions for translocation. Our measurements of fluid secretion rate, ion fluxes and electrophysiological responses to serotonin show that fluid secretion in K+-free saline is bumetanide sensitive and hydrochlorothiazide insensitive. Dose-response curves of secretion rate versus bumetanide concentration were identical for tubules bathed in K+-free and control saline with IC50 values of 2.6 x 10(-6) mmol l(-1) and 2.9 x 10(-6) mmol l(-1), respectively. Double-reciprocal plots of K+ flux versus bathing saline K+ concentration showed that increasing Na+ concentration in the bathing fluid increased Kt but had no effect on Jmax, consistent with competitive inhibition of K+ transport by Na+. We propose that the competition between Na+ and K+ for transport by the bumetanide-sensitive transporter is part of an autonomous mechanism by which Malpighian tubules regulate haemolymph K+ concentration.

Authors+Show Affiliations

Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada, L8S 4K1.No affiliation info availableNo affiliation info available

Pub Type(s)

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

Language

eng

PubMed ID

15371478

Citation

Ianowski, Juan P., et al. "Na+ Competes With K+ in Bumetanide-sensitive Transport By Malpighian Tubules of Rhodnius Prolixus." The Journal of Experimental Biology, vol. 207, no. Pt 21, 2004, pp. 3707-16.
Ianowski JP, Christensen RJ, O'Donnell MJ. Na+ competes with K+ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus. J Exp Biol. 2004;207(Pt 21):3707-16.
Ianowski, J. P., Christensen, R. J., & O'Donnell, M. J. (2004). Na+ competes with K+ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus. The Journal of Experimental Biology, 207(Pt 21), 3707-16.
Ianowski JP, Christensen RJ, O'Donnell MJ. Na+ Competes With K+ in Bumetanide-sensitive Transport By Malpighian Tubules of Rhodnius Prolixus. J Exp Biol. 2004;207(Pt 21):3707-16. PubMed PMID: 15371478.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Na+ competes with K+ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus. AU - Ianowski,Juan P, AU - Christensen,Robert J, AU - O'Donnell,Michael J, PY - 2004/9/17/pubmed PY - 2005/1/19/medline PY - 2004/9/17/entrez SP - 3707 EP - 16 JF - The Journal of experimental biology JO - J Exp Biol VL - 207 IS - Pt 21 N2 - We examined the effects of bathing saline Na+/K+ ratio, bumetanide and hydrochlorothiazide on fluid and ion transport by serotonin-stimulated Malpighian tubules of Rhodnius prolixus. Previous pharmacological and electrophysiological studies indicate that a bumetanide-sensitive Na+/K+/2Cl- cotransporter is the primary route for basolateral ion entry into the cell during fluid secretion. The goal of this study was to resolve the apparent conflict between relatively high secretion rates by tubules bathed in K+-free saline and the evidence that Na+/K+/2Cl- cotransporters described in other systems have an absolute requirement for all three ions for translocation. Our measurements of fluid secretion rate, ion fluxes and electrophysiological responses to serotonin show that fluid secretion in K+-free saline is bumetanide sensitive and hydrochlorothiazide insensitive. Dose-response curves of secretion rate versus bumetanide concentration were identical for tubules bathed in K+-free and control saline with IC50 values of 2.6 x 10(-6) mmol l(-1) and 2.9 x 10(-6) mmol l(-1), respectively. Double-reciprocal plots of K+ flux versus bathing saline K+ concentration showed that increasing Na+ concentration in the bathing fluid increased Kt but had no effect on Jmax, consistent with competitive inhibition of K+ transport by Na+. We propose that the competition between Na+ and K+ for transport by the bumetanide-sensitive transporter is part of an autonomous mechanism by which Malpighian tubules regulate haemolymph K+ concentration. SN - 0022-0949 UR - https://www.unboundmedicine.com/medline/citation/15371478/Na+_competes_with_K+_in_bumetanide_sensitive_transport_by_Malpighian_tubules_of_Rhodnius_prolixus_ L2 - http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=15371478 DB - PRIME DP - Unbound Medicine ER -