Acyl-Coenzyme A Causes Ca2+ Release in Pancreatic Acinar Cells

Abstract

Cytosolic Ca 2ϩ is an important regulator of many cell functions. Increases in cytosolic Ca 2ϩ occur by release of Ca 2ϩ from intracellular stores located in the endoplasmic reticulum. There are at least two types of Ca 2ϩ channels that regulate release from Ca 2ϩ stores: an inositol 1,4,5-trisphosphate (IP 3 ) 1 -sensitive channel (IP 3 receptor) and a ryanodine-sensitive channel (ryanodine receptor). As its name implies, IP 3 opens the IP 3 receptor and is used as a second messenger in many cells to release Ca 2ϩ . The ryanodine-sensitive channel (RyR) is responsible for calcium-induced calcium release (CICR).There is solid evidence for CICR in the pancreatic acinar cell (1, 2), in addition to some of the first evidence for IP 3 signaling (3). CICR is important in the acinar cell during submaximal agonist stimulation. Low doses of cholecystokinin or carbachol induce Ca 2ϩ waves and oscillations (4). In the two pool model of oscillations, IP 3 acts as an initiator of Ca 2ϩ release triggering CICR, generating the Ca 2ϩ spike (5). Discovery of regulators of CICR are important for full understanding of Ca 2ϩ signaling. There is a growing list of RyR regulators including, caffeine, cyclic ADP-ribose, procaine, spermine, and long chain acyl-CoA derivatives (6). Even though CICR has been established for the pancreatic acinar cell, there is conflicting data regarding the effects of ryanodine and caffeine (classic activators of the RyR). In rat pancreatic acinar cells, there is data supporting activation (7), inhibition (8), and lack of effect (2) of ryanodine and/or caffeine. Unlike ryanodine and caffeine, cyclic ADP-ribose, another activator of the RyR, is naturally occurring in many cell types, but some mammalian cells, including pancreatic acinar cells, are far less sensitive to cADPR than sea urchin eggs (9). Acyl-CoA are also naturally occurring compounds that release Ca 2ϩ (10), but there is no data regarding the presence or the effects of acyl-CoA on acinar cell Ca 2ϩ movements. To study the regulation of CICR in pancreas, we tested the effect of acyl-CoA on Ca 2ϩ release mechanisms in permeablized rat pancreatic acini. Also the effect of acyl-CoA in relation to those of ryanodine and caffeine was measured. EXPERIMENTAL PROCEDURESIsolation of Acini-Rat pancreatic acini were isolated as described previously (11). The rats were sacrificed by CO 2 induced asphyxiation, followed by cervical dislocation. The pancreas was removed and injected with a collagenase, digestion buffer (in mM: 95 NaCl, 6 KCl, 1 MgCl 2 , 4 sodium pyruvate, 11 glucose, 2 NaH 2 PO 4 , 4 sodium fumarate, 5 glutamate, 25 HEPES, 2 CaCl 2 , 2 glutamine, also included 20 units/ml purified collagenase, 2 ϫ minimal Eagle's amino acids, and 0.2% (w/v) bovine serum albumin (BSA) (pH 7.4) (NaOH)). The pancreas was incubated 45 min at 37°C in a shaking water bath (Dubnoff, Precision Scientific, Chicago, IL) in 5 ml of digestion buffer with three changes of buffer. Acini were dispersed by passage through large and small bore glass pipettes and then washed...

Multiple isoforms of the ryanodine receptor are expressed in rat pancreatic acinar cells

“…Thorn et al [11] found that 10 mM caffeine increased Ca# + , and that ryanodine could both potentiate and block Ca# + release. In our hands, ryanodine and caffeine added to permeablized acini had little effect on their own, but potentiated the effect of palmitoyl-CoA on Ca# + release [12]. On the other hand, we found that cADP-ribose had little effect on Ca# + release, in contrast to the study by Thorn et al [11].…”

“…We have shown previously that palmitoyl-CoA causes Ca# + release from a heparin-insensitive store, and that release is potentiated by low-dose ryanodine and caffeine [12]. These studies imply a functional non-Ins(1,4,5) P $ -receptor Ca# + channel with characteristics typical of RyRs.…”

“…Ito et al [34] found that micromolar spikes of intracellular [Ca# + ] were necessary for inducing exocytosis of zymogen granules. Our previous results suggest that Ca# + stores gated by RyRs account for more than 50 % of the total releasable intracellular Ca# + [12]. Therefore, multiple RyR isoforms in the pancreatic acinar cell may serve to amplify agonist-mediated Ca# + release and raise intracellular [Ca# + ] high enough and fast enough to cause the secretory response.…”

Involvement of Ca2+-mediated apoptotic signals in palmitate-induced MIN6N8a beta cell death

“…However, because chronic exposure of beta cells to FFAs, especially in the presence of glucose, prefers lipogenic pathway, LC-CoAs, metabolic intermediates in the lipogenic pathway, are thought to be candidates for the elevation of [Ca 2+ ] i . In particular, palmitoyl-CoA has been reported to elicit the elevation of [Ca 2+ ] i by directly regulating VDCC (Warnotte et al, 1994;Haber et al, 2003) or by mobilizing calcium from internal calcium stores (Fitzsimmons et al, 1997). Another study reports that the influx of Ca 2+ through VDCC plays a role in sustaining palmitate-evoked Ca 2+ elevation (Remizov et al, 2003).…”

Phosphatidylinositol 3-kinase regulates Ca2+signaling in pancreatic acinar cells through inhibition of sarco(endo)plasmic reticulum Ca2+-ATPase

“…The peak and plateau [Ca 2ϩ ] i responses are thought to be at least in part responsible for the pathological effect of high-dose CCK on exocrine pancreas (35,51,54 (3,4,8,24,37). Besides Ins(1,4,5)P 3 , cADP-ribose, nicotinic acid adenine dinucleotide phosphate (NAADP), and fatty acid ethyl esters are able to release Ca 2ϩ from intracellular stores through effects on Ca 2ϩ -regulated ryanodine receptors (RyRs) and NAADP receptors (8,15,24,51,55). Current evidence (8,24,37,44) suggests that Ins(1,4,5)P 3 and its receptors act to trigger Ca 2ϩ release from the ER, whereas the other signals act to amplify the Ca 2ϩ signals.…”