Calcyclin, a calcium-binding protein, which regulates insulin secretion from the permeabilized pancreatic beta-cell.

Abstract

Although it is widely accepted that an increase in intracellular Ca2+ is a crucial event in the stimulus-secretion coupling in the pancreatic β-cell [1], we have limited knowledge on the later steps in the signal transduction pathway. Calcium binding proteins are considered to be involved in the control of Ca2+-dependent cellular functions including hormone release [2]. Various types of calcium-binding proteins such as calmodulin, calbindin and S-100b protein are identified in the islet cells biochemically or immunohistochemically [3,4]. Calmodulin, the best characterized calcium binding protein, was demonstrated to exist in the pancreatic islet cells by Sugden et al [5]. The pancreatic β-cell possesses the kinase activity which is dependent on Ca2+/calmodulin [6]. Involvement of calmodulin and calmodulin-dependent protein kinases in insulin release has been suggested mainly based on the inhibitory effect of calmodulin antagonists on the release [7,8,9], albeit there is the argument against this idea [10].