Bile acids activate ryanodine receptors in pancreatic acinar cells via a direct allosteric mechanism

The earliest critical event of pancreatitis is a long lasting high amplitude rise of intracellular Ca(2+) concentration of the acinar cell, which can be triggered by high concentration of bile acids. Although, Ca(2+)-release through ryanodine receptors (RyR) is involved in the process, the significance and the exact mechanism of bile acid's action on RyR has not been fully elucidated yet. Therefore, we aimed to test with various techniques and aspects whether bile acids exert a direct effect on RyR and SERCA pump. Our data show that taurocholic acid (TCA)-induced Ca(2+) release in pancreatic acinar cells was significantly reduced by the RyR antagonist dantrolene. Further, we show that TCA enhanced RyR's (3)H-ryanodine binding and triggered robust Ca(2+)-release from RyR-enriched vesicles in the pathologically relevant concentration range. RyR single channel current analysis demonstrated that 200μM TCA induced a 5-fold increase in the channel's open probability and caused a significant lengthening of the mean open time. TCA also suppressed Ca(2+)-uptake rate and ATP-ase activity of SERCA-enriched vesicles, but interestingly, failed to decrease Ca(2+) elimination rate in intact cells. Overall, our results strongly suggest that TCA opens RyR by an allosteric mechanism, which contribute significantly to bile acid-induced pathologic Ca(2+)-leak from the endoplasmic reticulum in pancreatic acinar cells

Transcriptome‐based screening of ion channels and transporters in a migratory chondroprogenitor cell line isolated from late‐stage osteoarthritic cartilage

Chondrogenic progenitor cells (CPCs) may be used as an alternative source of cells with potentially superior chondrogenic potential compared to mesenchymal stem cells (MSCs), and could be exploited for future regenerative therapies targeting articular cartilage in degenerative diseases such as osteoarthritis (OA). In this study, we hypothesised that CPCs derived from OA cartilage may be characterised by a distinct channelome. First, a global transcriptomic analysis using Affymetrix microarrays was performed. We studied the profiles of those ion channels and transporter families that may be relevant to chondroprogenitor cell physiology. Following validation of the microarray data with quantitative reverse transcription-polymerase chain reaction, we examined the role of calcium-dependent potassium channels in CPCs and observed functional large-conductance calcium-activated potassium (BK) channels involved in the maintenance of the chondroprogenitor phenotype. In line with our very recent results, we found that the KCNMA1 gene was upregulated in CPCs and observed currents that could be attributed to the BK channel. The BK channel inhibitor paxilline significantly inhibited proliferation, increased the expression of the osteogenic transcription factor RUNX2, enhanced the migration parameters, and completely abolished spontaneous Ca2+ events in CPCs. Through characterisation of their channelome we demonstrate that CPCs are a distinct cell population but are highly similar to MSCs in many respects. This study adds key mechanistic data to the in-depth characterisation of CPCs and their phenotype in the context of cartilage regeneration

Expression of BK channels and Na+-K+ pumps in the apical membrane of lacrimal acinar cells suggests a new molecular mechanism for primary tear-secretion

L

Expression of BK channels and Na+-K+ pumps in the apical membrane of lacrimal acinar cells suggests a new molecular mechanism for primary tear-secretion

L

TRPM4 links calcium signaling to membrane potential in pancreatic acinar cells

TRPM4 is a Ca2+-activated nonselective cation channel that mediates membrane depolarization. Although, a current with the hallmarks of a TRPM4-mediated current has been previously reported in pancreatic acinar cells (PAC), the role of TRPM4 in the regulation of acinar cell function has not yet been explored. In the present study, we identify this TRPM4 current and describe its role in context of Ca2+ signaling of PACs using pharmacological tools and TRPM4-deficient mice. We found a significant Ca2+-activated cation current in PACs that was sensitive to the TRPM4 inhibitors 9-phenanthrol and CBA (4-Chloro-2-[[2-(2-chlorophenoxy)acetyl]amino]benzoic acid). We demonstrated that the CBA-sensitive current was responsible for a Ca2+-dependent depolarization of PACs from a resting membrane potential of -44.4 ± 2.9 to -27.7 ± 3 mV. Furthermore, we showed that Ca2+ influx was higher in the TRPM4 KO- and CBA-treated PACs than in control cells. As hormone induced repetitive Ca2+ transients partially rely on Ca2+ influx in PACs, the role of TRPM4 was also assessed on Ca2+ oscillations elicited by physiologically relevant concentrations of the cholecystokinin analogue cerulein. These data show that the amplitude of Ca2+ signals were significantly higher in TRPM4 KO than in control PACs. Our results suggest that PACs are depolarized by TRPM4 currents to an extent that results in a significant reduction of the inward driving force for Ca2+. In conclusion, TRPM4 links intracellular Ca2+ signaling to membrane potential as a negative feedback regulator of Ca2+ entry in PACs