Expression of the Novel Epithelial Ca²⁺ Channel ECaC1 in Rat Pancreatic Islets

The epithelial Ca²⁺ channel, ECaC1, is primarily expressed in the apical membrane of vitamin D-responsive tissues. This study characterizes for the first time the presence of this novel channel in pancreatic tissue by reverse transcriptase-polymerase chain reaction and immunohistochemistry. In addition, the expression of ECaC1 was investigated in an animal model for Type 2 diabetes mellitus, the Zucker diabetic fatty (ZDF) rat. Identical staining patterns for ECaC1 and insulin were observed, whereas no co-localization of ECaC1 with glucagon was found. ECaC1, insulin, and prohormone convertase 1 (a neuroendocrine endoprotease expressed in secretory granules) showed a similar punctate staining. ECaC1 co-localized with the Ca²⁺ binding protein calbindin-D₂8K in the β-cells. Furthermore, in contrast to wild-type rats, in ZDF rats aging led to a progressive decrease in both insulin and ECaC1 staining. Plasma 1,25-dihydroxyvitamin D₃ levels were similar in both control and ZDF rats and decreased with aging. Taken together, our findings indicate that this novel Ca²⁺ channel may play a role in the regulation of endocrine Ca²⁺ homeostasis.