Resveratrol Inhibits Electrical Activity and Insulin Release from Insulinoma Cells by Block of Voltage-Gated Ca²⁺ Channels and Swelling-Dependent Cl^- Currents

Abstract

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 β-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 μM) to elicit membrane depolarizations and electrical activity. Application of RV (50 μM) 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 Ca²⁺ 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 Ca²⁺- and swelling-dependent Cl^- currents despite the inhibition of K_ATP currents.

The Phytostilbene Resveratrol Induces Apoptosis in INS-1E Rat Insulinoma Cells

“…In isolated pancreatic islets resveratrol has been shown to reversibly and dosedependently inhibit insulin secretion in a protein kinase C dependent manner consistent with a repression of the amplifying pathway of insulin release [15][16][17]. In a recent study we have shown a reversible suppression of glucose-, hypotonicity-and tolbutamide-induced membrane depolarization and electrical activity by resveratrol in INS-1E rat insulinoma cells and a complete inhibition of glucose-induced insulin release within 1 hour, suggesting a block of the triggering pathway of insulin secretion [18].…”

“…In our previous work we found that resveratrol, besides blocking glucose/ swelling-dependent Cl -channels, also inhibits K ATP channels [18]. The fact that this inhibition does obviously not prevent AVD implies further ion extrusion pathways to be involved in AVD in INS-1E cells.…”

“…This effect was prevented by an anti-insulin antibody, PI3K inhibition or by the L-type Ca 2+ channel blocker nifedipine. Importantly, we previously demonstrated that in INS-1E cells resveratrol inhibits stimulus-secretioncoupling by blocking L-and T-type Ca 2+ channels and glucose/swelling-dependent Cl -channels [18] so that it is feasible that the proapoptotic effect of resveratrol is the result of an indirect inhibition of insulin receptor signaling by a suppression of insulin release and a direct inhibition of promitotic/antiapoptotic Akt signaling. Insulin receptor expression in INS-1E cells was confirmed by reverse transcriptase and real-time PCR and remained unaltered within 48 hours in resveratrol treated cells (data not shown).…”

The H+/K+ ATPase Inhibitor SCH-28080 Inhibits Insulin Secretion and Induces Cell Death in INS-1E Rat Insulinoma Cells

“…Therefore, we recorded voltage-activated Ca 2+ current (ICa v ). Using Ba 2+ as charge carrier, voltage ramps elicited low- and high-voltage (T- and L-type)-activated Ca 2+ currents, as previously described in INS-1E and INS-1 cells [42, 43]. While T-type currents ran down upon repeated activation, L-type currents persisted with peak amplitudes at -13.3 mV (n=14), as shown in Fig.…”

Resveratrol Potentiates Glucose-stimulated Insulin Secretion in INS-1E β-Cells and Human Islets through a SIRT1-dependent Mechanism

“…In MIN6 insulinoma cells, it was shown that resveratrol enhances insulin secretion by blocking K ATP and K V channels (28). Conversely, resveratrol was reported to inhibit insulin secretion in rat pancreatic islets (29) and to counteract stimulus-induced depolarization of INS-1E cells (56). A close link between resveratrol and SIRT1 has been demonstrated in muscles and adipose tissues (19).…”