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+]i 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 betaTC-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.

SHAHIDUL ISLAM, M.D., Leibiger, I., Leibiger, B., Rossi, D., Sorrentino, V., Ekstrom, T., et al. (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 [10.1073/pnas.95.11.6145].

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

ROSSI, D.;SORRENTINO, V.;
1998

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+]i 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 betaTC-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.
SHAHIDUL ISLAM, M.D., Leibiger, I., Leibiger, B., Rossi, D., Sorrentino, V., Ekstrom, T., et al. (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 [10.1073/pnas.95.11.6145].
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11365/23127
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