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

Abstract

ABSTRACT2؉ spikes that were enhanced by 3,9-dimethylxanthine, an activator of RYs. Analysis of RNA from islets and insulin-secreting ␤TC-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 (RY 2 ). We conclude that in situ activation of RY 2 in beta cells requires cAMPdependent phosphorylation, a process that recruits the receptor in a functionally operative form.Ryanodine receptors (RY) are Ca 2ϩ channels in the endoplasmic reticulum (ER) composed of four Ϸ550-kDa RY protomers and four molecules of FKBP12 or FKBP12.6. The latter are isoforms of the 12-kDa binding protein for the immunosuppressant drug FK506. cDNAs for three RYs have been cloned. Ryanodine RY 1 , RY 2 , and RY 3 receptors are products of three genes (1). Truncated and splice variants of RYs have been described, all of which might associate in the form of homo-or heterotetramers to produce large diversity of the channels. FKBP12 and FKBP12.6 associate with RY 1 and RY 2 , respectively, and stabilize the channel (2). Studies in cell-free systems have demonstrated that activity of RYs can be modulated by numerous factors including phosphorylationdephosphorylation, Ca 2ϩ

Nicotinic acid-adenine dinucleotide phosphate-sensitive calcium stores initiate insulin signaling in human beta cells

“…4B). Human beta cells also possess Ca 2ϩ stores mobilized via RyR2 activation (25). Indeed, 1-10 nM ryanodine, which locks RyR in an open subconductance state, evoked Ca 2ϩ signals in beta cells with a maximal amplitude of 117 Ϯ 24 nM, confirming the presence of functional ryanodine-sensitive Ca 2ϩ stores in our preparations (n ϭ 21; not shown).…”

Ca2+-induced Ca2+ release by activation of inositol 1,4,5-trisphosphate receptors in primary pancreatic β-cells

“…Both type 2 RyR mRNA and RyR protein are expressed in primary as well as clonal -cells [13][14][15]. Convincing evidence for functional RyRs come only from the clonal -cells RINm-5F [54], HIT-T15 [14], MIN6 [15] and INS-1 [17,18,55] in which caffeine exhibits the characteristic acute effect on Ca 2+ mobilization.…”

“…Another important mechanism is the Ca 2+ -induced Ca 2+ release (CICR), by which a depolarizationdependent rise of [Ca 2+ ] i may become amplified by Ca 2+ release from the ER [12]. Even though RyRs are expressed in -cells [13][14][15], the physiological role of cADPr and RyRs remains controversial [16]. Nevertheless, there are several suggestions that RyRs mediate CICR in -cells [12,14,[17][18][19].…”

Ca2+-induced Ca2+ Release from the Endoplasmic Reticulum Amplifies the Ca2+ Signal Mediated by Activation of Voltage-gated L-type Ca2+ Channels in Pancreatic β-Cells

“…the plasma membrane Ca 2ϩ channels and the ER Ca 2ϩ channels. ␤-Cells possess the requisite molecular components required for mediating CICR (5,10). However, the issue of whether ER Ca 2ϩ stores and the associated Ca 2ϩ channels participate in the depolarization-induced Ca 2ϩ signaling in intact ␤-cells has remained an open question.…”