In situ activation of the type 2 ryanodine receptor in pancreatic beta cells requires cAMP-dependent phosphorylation

Md Shahidul Islam, Ingo Leibiger, Barbara Leibiger, Daniela Rossi, Vincenzo Sorrentino, Tomas J. Ekström, Håkan Westerblad, Francisco H. Andrade, Per Olof Berggren

Research output: Contribution to journalArticle

90 Scopus citations

Abstract

Molecular mechanisms that regulate in situ activation of ryanodine receptors (RY) in different cells are poorly understood. Here we demonstrate that caffeine (10 mM) released Ca2+ from the endoplasmic reticulum (ER) in the form of small spikes in only 14% of cultured fura-2 loaded beta cells from ob/ob mice. Surprisingly, when forskolin, an activator of adenylyl cyclase was present, caffeine induced larger Ca2+ spikes in as many as 60% of the cells. Forskolin or the phosphodiesterase-resistant PKA activator Sp- cAMPS alone did not release Ca2+ from ER. 4-Chloro-3-ethylphenol (4-CEP), an agent that activates RYs in other cell systems, released Ca2+ from ER, giving rise to a slow and small increase in [Ca2+]1 in beta cells. Prior exposure of cells to forskolin or caffeine (5 mM) qualitatively altered Ca2+ release by 4-CEP, giving rise to Ca2+ spikes. In glucose-stimulated beta cells forskolin induced Ca2+ spikes that were enhanced by 3,9- dimethylxanthine, an activator of RYs. Analysis of RNA from islets and insulin-secreting βTC-3-cells by RNase protection assay, using type-specific RY probes, revealed low-level expression of mRNA for the type 2 isoform of the receptor (RY2). We conclude that in situ activation of RY2 in beta cells requires cAMP-dependent phosphorylation, a process that recruits the receptor in a functionally operative form.

Original languageEnglish (US)
Pages (from-to)6145-6150
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume95
Issue number11
DOIs
StatePublished - May 26 1998

Keywords

  • Caffeine
  • Calcium
  • Islets of Langerhans

ASJC Scopus subject areas

  • Genetics
  • General

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    Islam, M. S., Leibiger, I., Leibiger, B., Rossi, D., Sorrentino, V., Ekström, T. J., Westerblad, H., Andrade, F. H., & Berggren, P. O. (1998). In situ activation of the type 2 ryanodine receptor in pancreatic beta cells requires cAMP-dependent phosphorylation. Proceedings of the National Academy of Sciences of the United States of America, 95(11), 6145-6150. https://doi.org/10.1073/pnas.95.11.6145