Activation of the plasma membrane Ca2+ pump during agonist stimulation of pancreatic acini

Bin Xian Zhang, Hong Zhao, Peggy Loessberg, Shmuel Muallem

Research output: Contribution to journalArticle

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Abstract

The role of internal stores and plasma membrane Ca2+ pumps in controlling [Ca2+]i during agonist stimulation and their regulation by agonists are not well understood. We report here measurements of intracellular ([Ca2+]i) and extracellular ([Ca2+]o) Ca2+ concentrations in agonist-stimulated pancreatic acini in an effort to directly address these questions. Stimulation of acini suspended in Ca2+-free or Ca2+-containing medium with Ca2+ mobilizing agonists resulted in a typical transient increase in [Ca2+]i. Thapsigargin, a specific inhibitor of internal Ca2+ pumps, inhibited the rate of [Ca2+]i reduction after agonist stimulation by approximately 40%. Under the same conditions, thapsigargin had no effect on the rate of the unidirectional Ca efflux across the plasma membrane as revealed by measurements of [Ca2+]o. These findings suggest that internal Ca2+ pumps actively remove Ca2+ from the cytosol during continued agonist stimulation. The correlation between the reduction in [Ca2+]i and the increase in [Ca2+]., showed that Ca2+ efflux from cells stimulated with agonist and thapsigargin represent Ca2+ efflux across the plasma membrane. Inhibition of cells exposed to agonist and thapsigargin with a specific antagonist sharply reduced the rates of the [Ca2+]. decrease and the accompanied [Ca2+]o increase. Hence, at comparable [Ca2+]i, Ca2+ efflux from stimulated cells was about 3-fold faster than that from resting cells, indicating that agonists directly activate the plasma membrane Ca2+ pump. To study the role of [Ca2+]. increase in plasma membrane Ca2+ pump activation the acini were loaded with 1,2-bis-(2-aminophenoxyethane- N,N,N′ ,N′) - tetraacetic acid (BAPTA), and [Ca2+]o was measured during agonist stimulation. Surprisingly, although BAPTA completely prevented the increase in [Ca2+]i, Ca2+ efflux rate was reduced by only 34%. These findings provide the first evidence for Ca2+-independent activation of the plasma membrane Ca2+ pump by Ca2+ mobilizing agonists.

Original languageEnglish (US)
Pages (from-to)15419-15425
Number of pages7
JournalJournal of Biological Chemistry
Volume267
Issue number22
StatePublished - Aug 5 1992
Externally publishedYes

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Cell membranes
Thapsigargin
Chemical activation
Cell Membrane
Pumps
Cytosol
Cells
Acids

ASJC Scopus subject areas

  • Biochemistry

Cite this

Zhang, B. X., Zhao, H., Loessberg, P., & Muallem, S. (1992). Activation of the plasma membrane Ca2+ pump during agonist stimulation of pancreatic acini. Journal of Biological Chemistry, 267(22), 15419-15425.

Activation of the plasma membrane Ca2+ pump during agonist stimulation of pancreatic acini. / Zhang, Bin Xian; Zhao, Hong; Loessberg, Peggy; Muallem, Shmuel.

In: Journal of Biological Chemistry, Vol. 267, No. 22, 05.08.1992, p. 15419-15425.

Research output: Contribution to journalArticle

Zhang, BX, Zhao, H, Loessberg, P & Muallem, S 1992, 'Activation of the plasma membrane Ca2+ pump during agonist stimulation of pancreatic acini', Journal of Biological Chemistry, vol. 267, no. 22, pp. 15419-15425.
Zhang, Bin Xian ; Zhao, Hong ; Loessberg, Peggy ; Muallem, Shmuel. / Activation of the plasma membrane Ca2+ pump during agonist stimulation of pancreatic acini. In: Journal of Biological Chemistry. 1992 ; Vol. 267, No. 22. pp. 15419-15425.
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abstract = "The role of internal stores and plasma membrane Ca2+ pumps in controlling [Ca2+]i during agonist stimulation and their regulation by agonists are not well understood. We report here measurements of intracellular ([Ca2+]i) and extracellular ([Ca2+]o) Ca2+ concentrations in agonist-stimulated pancreatic acini in an effort to directly address these questions. Stimulation of acini suspended in Ca2+-free or Ca2+-containing medium with Ca2+ mobilizing agonists resulted in a typical transient increase in [Ca2+]i. Thapsigargin, a specific inhibitor of internal Ca2+ pumps, inhibited the rate of [Ca2+]i reduction after agonist stimulation by approximately 40{\%}. Under the same conditions, thapsigargin had no effect on the rate of the unidirectional Ca efflux across the plasma membrane as revealed by measurements of [Ca2+]o. These findings suggest that internal Ca2+ pumps actively remove Ca2+ from the cytosol during continued agonist stimulation. The correlation between the reduction in [Ca2+]i and the increase in [Ca2+]., showed that Ca2+ efflux from cells stimulated with agonist and thapsigargin represent Ca2+ efflux across the plasma membrane. Inhibition of cells exposed to agonist and thapsigargin with a specific antagonist sharply reduced the rates of the [Ca2+]. decrease and the accompanied [Ca2+]o increase. Hence, at comparable [Ca2+]i, Ca2+ efflux from stimulated cells was about 3-fold faster than that from resting cells, indicating that agonists directly activate the plasma membrane Ca2+ pump. To study the role of [Ca2+]. increase in plasma membrane Ca2+ pump activation the acini were loaded with 1,2-bis-(2-aminophenoxyethane- N,N,N′ ,N′) - tetraacetic acid (BAPTA), and [Ca2+]o was measured during agonist stimulation. Surprisingly, although BAPTA completely prevented the increase in [Ca2+]i, Ca2+ efflux rate was reduced by only 34{\%}. These findings provide the first evidence for Ca2+-independent activation of the plasma membrane Ca2+ pump by Ca2+ mobilizing agonists.",
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