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  H+-dependent calcium uptake into an IP3-sensitive calcium pool from rat parotid gland

Thévenod, F., & Schulz, I. (1988). H+-dependent calcium uptake into an IP3-sensitive calcium pool from rat parotid gland. American Journal of Physiology, 255((4 Pt 1)), G429-G440. doi:10.1152/ajpgi.1988.255.4.G429.

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 Creators:
Thévenod, Frank1, Author           
Schulz, Irene1, Author           
Affiliations:
1Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society, ou_2068297              

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 Abstract: In permeabilized parotid cells and in isolated membrane vesicles from parotid endoplasmic reticulum (ER), Mg-ATP-dependent Ca2+ uptake was measured using a Ca2+-specific macroelectrode and 45Ca2+, respectively. Mg-ATP-dependent Ca2+ uptake was inhibited by vanadate (2 x 10-3 mol/l) by approximately 45% in permeabilized cells and by approximately 70% in membrane vesicles from ER during the initial 10 min. After this lag phase, Ca2+ uptake increased and low steady-state free [Ca2+] of approximately 3 x 10-7 mol/l was still reached in presence of vanadate within 30-40 min. Subsequent addition of inositol 1,4,5-trisphosphate (IP3) caused a similar Ca2+ release compared with control. This indicates that in presence of vanadate an IP3-sensitive Ca2+ pool was filled. However, when protonophores, such as nigericin or carbonyl cyanide-m-chlorophenylhydrazone, were added in addition to vanadate, this low steady-state free [Ca2+] was not reached. 45Ca2+ uptake was reduced by approximately 70% within 60 min, and IP3 did not cause 45Ca2+ release when given subsequently, indicating that filling of an IP3-sensitive Ca2+ pool was prevented. Mg-ATP-driven H+ uptake into ER vesicles, as estimated with acridine orange, was abolished by protonophores and by the H+-ATPase blockers N-ethylmaleimide and Dio 9 but was unaltered by vanadate. Preincubation of ER vesicles in a medium without Ca2+, but with vanadate and with Mg-ATP to generate an H+ gradient, allowed demonstration of 45Ca2+ uptake from a medium that did not contain ATP. The cation sequence in absence of vanadate for support of Mg-ATP-dependent 45Ca2+uptake was K++ greater than Na+ greater than Li+ = choline+ and, in presence of vanadate, was choline+ greater than Li+ = Na+ greater than K+. A preformed H+ gradient dissipated more rapidly in presence of K+ compared with choline+, probably due to an intrinsic K+ permeability of ER membrane. Our data indicate that both a Ca2+ and a H+ pump are located in a compartment of ER that is also sensitive to IP3. Ca2+ uptake is coupled to an H+ gradient that is generated by the H+ pump and most likely occurs via Mg-ATP-driven Ca2+-H+ countertransport but to some extent can also operate in absence of ATP at the expense of the H+ gradient.

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Language(s): eng - English
 Dates: 1987-07-101988-05-161988-10-10
 Publication Status: Issued
 Pages: 12
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1152/ajpgi.1988.255.4.G429
PMID: 3263053
 Degree: -

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Title: American Journal of Physiology
Source Genre: Journal
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Publ. Info: Bethesda, Md., etc. : American Physiological Society [etc.]
Pages: - Volume / Issue: 255 ((4 Pt 1)) Sequence Number: - Start / End Page: G429 - G440 Identifier: ISSN: 0002-9513
CoNE: https://pure.mpg.de/cone/journals/resource/954926936682