NDLI: Phosphatidylinositol 4,5-bisphosphate degradation inhibits the Na+/bicarbonate cotransporter NBCe1-B and -C variants expressed in Xenopus oocytes

Content Provider	PubMed Central
Author	Thornell, Ian M. Bevensee, Mark O.
Copyright Year	2014
Abstract	The electrogenic Na+/bicarbonate cotransporter (NBCe1) of the Slc4 gene family is a powerful regulator of intracellular pH (pHi) and extracellular pH (pHo), and contributes to solute reabsorption and secretion in many epithelia. Using Xenopus laevis oocytes expressing NBCe1 variants, we have previously reported that the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) directly stimulates NBCe1-A in an excised macropatch, and indirectly stimulates NBCe1-B and -C in the intact oocyte primarily through inositol 1,4,5-trisphosphate (InsP3)/Ca2+. In the current study, we used the two-electrode voltage-clamp technique alone or in combination with pH/voltage-sensitive microelectrodes or confocal fluorescence imaging of plasma membrane PIP2 to characterize the PIP2 sensitivity of NBCe1-B and -C in whole oocytes by co-expressing a voltage-sensitive phosphatase (VSP) that decreases PIP2 and bypasses the InsP3/Ca2+ pathway. An oocyte depolarization that activated VSP only transiently stimulated the NBCe1-B/C current, consistent with an initial rapid depolarization-induced NBCe1 activation, and then a subsequent slower VSP-mediated NBCe1 inhibition. Upon repolarization, the NBCe1 current decreased, and then slowly recovered with an exponential time course that paralleled PIP2 resynthesis as measured with a PIP2-sensitive fluorophore and confocal imaging. A subthreshold depolarization that minimally activated VSP caused a more sustained increase in NBCe1 current, and did not lead to an exponential current recovery following repolarization. Similar results were obtained with oocytes expressing a catalytically dead VSP mutant at all depolarized potentials. Depleting endoplasmic reticulum Ca2+ did not inhibit the NBCe1 current recovery following repolarization from VSP activation, demonstrating that changes in InsP3/Ca2+ were not responsible. This study demonstrates for the first time that depleting PIP2 per se inhibits NBCe1 activity. The data in conjunction with previous findings implicate a dual PIP2 regulatory pathway for NBCe1 involving both PIP2 itself and generated InsP3/Ca2+.
Related Links	http://dx.doi.org/10.1113/jphysiol.2014.284307
Ending Page	558
Page Count	18
Starting Page	541
File Format	PDF
ISSN	14697793
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 3
Volume Number	593
Language	English
Publisher	BlackWell Publishing Ltd
Publisher Date	2015-02-01
Access Restriction	Open
Rights Holder	BlackWell Publishing Ltd
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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PIP2 hydrolysis stimulates the electrogenic Na+–bicarbonate cotransporter NBCe1-B and -C variants expressed in Xenopus laevis oocytes

Phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates the electrogenic Na/HCO3 cotransporter NBCe1-A expressed in Xenopus oocytes

Electrogenic Na/HCO3 Cotransporter (NBCe1) Variants Expressed in Xenopus Oocytes: Functional Comparison and Roles of the Amino and Carboxy Termini

Water transport by the human Na+-coupled glutamate cotransporter expressed in Xenopus oocytes

Passive water and urea permeability of a human Na+–glutamate cotransporter expressed in Xenopus oocytes

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