Methylamine and islet function: possible relationship to Ca2+-sensitive transglutaminase.

Pancreatic islet homogenates display Ca2+-dependent transglutaminase activity. Methylamine inhibits the enzyme activity, accumulates in intact islet cells, is incorporated in endogenous islet proteins, and inhibits glucose-stimulated insulin release. The inhibition by methylamine of both enzyme activity and insulin release is inversely related to the ambient Ca2+ concentration. Dimethylamine also inhibits transglutaminase activity and glucose-stimulated insulin release. However, trimethylamine, which does not affect transglutaminase activity, again inhibits glucose-stimulated insulin release, the latter inhibition being also inversely related to the Ca2+ concentration. It is concluded that the impairment of insulin release by methylamines is not necessarily linked to inhibition of transglutaminase activity.