Cyclosporin a, but not FK506, induces osmotic lysis of pancreas zymogen granules, intra-acinar enzyme release, and lysosome instability by activating K+ channel.

OBJECTIVES: The immunosuppressant tacrolimus (FK506) has improved pancreas allograft survival compared with cyclosporin A (CsA), possibly because of reduced acute pancreatitis following ischemia-reperfusion injury. Ion permeabilities in zymogen granule (ZG) membranes, including a KCNQ1 K channel, promote hormone-stimulated enzyme secretion. We investigated whether a differential modulation of ZG and lysosomal ion permeabilities and enzyme secretion by CsA/FK506 contributes to pancreatitis. METHODS: Rat ZGs and lysosomes were isolated by gradient centrifugation, ion permeabilities assayed by osmotic lysis, and single-channel currents recorded in a planar lipid bilayer. Amylase release was measured in permeabilized acini and lysosomal cathepsin B release detected by immunoblotting. RESULTS: CsA (1-10 µM), but not FK506, enhanced ZGs osmotic lysis by selectively increasing K permeability up to 5-fold. Zymogen granule membrane K channels showed ∼2-fold increased single-channel open probability with CsA only. Cyclosporin A selectively increased basal (∼2-fold), but not cholecystokinin-octapeptide (1 nM)-induced amylase secretion in K medium only. Cyclosporin A (5 µM), but not FK506, increased cathepsin B release from lysosomes. CONCLUSIONS: Cyclosporin A selectively opens the ZG K channel and induces cathepsin B release from lysosomes, which cause increased in situ lysis of ZGs and may aggravate or fuel acute allograft pancreatitis following hypoxia-reperfusion injury.

Resveratrol inhibits electrical activity and insulin release from insulinoma cells by block of voltage-gated Ca+ channels and swelling-dependent Cl- currents.

The phytostilbene resveratrol (RV) improves the metabolic state in animal models by increasing the insulin responsiveness of tissues and there is evidence that RV affects insulin secretion from native beta-cells and insulinoma cells. In whole cell patch clamp experiments on clonal rat INS-1E cells we used high extracellular glucose (20 mM), extracellular hypotonicity (30%) or tolbutamide (100 microM) to elicit membrane depolarizations and electrical activity. Application of RV (50 microM) repolarized the cells, terminated electrical activity and prevented the hypotonicity-induced depolarization. These effects were fully reversible and intermittent application of RV restored tolbutamide-induced electrical activity after desensitization. Glucose-induced depolarization was counteracted by RV in presence of iberiotoxin (50 nM), showing that the RV effect does not depend on BK(Ca) channel activation. RV dose-dependently inhibited K(ATP) currents, L- and T-type Ca(2+) currents and swelling-dependent Cl(-) currents evoked by either hypotonicity or high extracellular glucose--ion conductances crucially involved in regulating the electrical activity of insulin secreting cells. We further show that RV blunts glucose-induced, but not basal insulin release. Our results indicate that RV counteracts/prevents stimulus-induced cell membrane depolarization and electrical activity by blocking voltage-gated Ca(2+)- and swelling-dependent Cl(-) currents despite the inhibition of K(ATP) currents.