Calcium Dynamics During Physiological Acidification in Xenopus Oocyte

Calcium Dynamics During Physiological Acidification in Xenopus Oocyte Interplays between intracellular pH (pHi) and calcium ([Ca2+]i) variations remain unclear, though both proton and calcium homeostasis changes accompany physiological events such as Xenopus laevis oocyte maturation. In this report, we used NH4Cl and changes of extracellular pH (pHe) to acidify the cytosol in a physiological range. In oocytes voltage-clamped at −80 mV, NH4Cl triggered an inward current, the main component of which is a Ca2+-dependent chloride current. Calcium imaging confirmed that NH4Cl provoked a [Ca2+]i increase. The mobilized sources of calcium were discriminated using the triple-step protocol as a means to follow both the calcium-activated chloride currents (ICl-Ca) and the hyperpolarization- and acid-activated nonselective cation current (IIn). These currents were stimulated during external addition of NH4Cl. This upregulation was abolished by BAPTA-AM, caffeine and heparin. By both buffering pHi changes with MOPS and by inhibiting calcium influx with lanthanum, intracellular acidification, initiated by NH4Cl and extracellular acidic medium, was shown to trigger a [Ca2+]i increase through both calcium release and calcium influx. The calcium pathways triggered by pHe changes are similar to those activated by NH4Cl, thus suggesting that there is a robust signaling mechanism allowing the cell to adjust to variable environmental conditions. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

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Publisher
Springer-Verlag
Copyright
Copyright © 2010 by Springer Science+Business Media, LLC
Subject
Life Sciences; Human Physiology ; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-010-9290-1
Publisher site
See Article on Publisher Site

Abstract

Interplays between intracellular pH (pHi) and calcium ([Ca2+]i) variations remain unclear, though both proton and calcium homeostasis changes accompany physiological events such as Xenopus laevis oocyte maturation. In this report, we used NH4Cl and changes of extracellular pH (pHe) to acidify the cytosol in a physiological range. In oocytes voltage-clamped at −80 mV, NH4Cl triggered an inward current, the main component of which is a Ca2+-dependent chloride current. Calcium imaging confirmed that NH4Cl provoked a [Ca2+]i increase. The mobilized sources of calcium were discriminated using the triple-step protocol as a means to follow both the calcium-activated chloride currents (ICl-Ca) and the hyperpolarization- and acid-activated nonselective cation current (IIn). These currents were stimulated during external addition of NH4Cl. This upregulation was abolished by BAPTA-AM, caffeine and heparin. By both buffering pHi changes with MOPS and by inhibiting calcium influx with lanthanum, intracellular acidification, initiated by NH4Cl and extracellular acidic medium, was shown to trigger a [Ca2+]i increase through both calcium release and calcium influx. The calcium pathways triggered by pHe changes are similar to those activated by NH4Cl, thus suggesting that there is a robust signaling mechanism allowing the cell to adjust to variable environmental conditions.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Aug 18, 2010

References

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