Aim: 

Permeants and hypotonicity are believed to induce exocytosis via the same mechanism – cell swelling. This study was performed to compare their effect on insulin release from rat insulinoma cell lines INS-1 and INS-1E.

Methods: 

Static incubations experiments were performed on all three experimental systems (30% hypotonicity, ethanol and urea).

Results: 

In Ca²⁺containing medium hypotonicity induced insulin release from pancreatic islets and INS-1 cells but inhibited insulin secretion from cell line INS-1E. Noradrenalin inhibits glucose-induced but not hypotonicity (swelling)-induced insulin release from islets and INS-1 cells. Ethanol and urea (in isosmolar medium) induced distinct cell swelling in both tumour cell lines. Ethanol (in 40, 80 and 160 mmol/l concentration) in isosmotic medium stimulated insulin secretion from both cell types. Ethanol stimulation was abolished by 1 mmol/l noradrenaline. In contrary to previous data our result show suppressive effect of urea (in 40, 80 and 160 mmol/l in isosmolar medium) on insulin secretion from INS-1 and INS-1E cells.

Conclusion: 

Mechanism of ethanol-induced insulin secretion in these cell lines differs from that induced by hypotonicity; it was not mediated by its permeant effect. Signaling pathway for ethanol stimulation shares noradrenaline sensitive step(s) with glucose-induced insulin secretion. The inhibiting effect of urea in tumour cell lines should utilize different mechanism.

Acknowledgements: 

The work was supported by the project 2/6158/26 of the Grant Agency of Ministry of Education of the Slovak republic and Slovak Academy of Sciences (VEGA), project APVV 0235-06 and project of CE SAV CENDO