Age-Dependent Expression of Protein Kinase C Isoforms in Rat Islets

The appearance of the biphasic insulin secretory response several days after birth suggests that maturation of a critical step in stimulus-secretion coupling occurs during the early neonatal period. To clarify the role of protein kinase C (PKC) during this time, we examined the pancreatic islets of adult, 3-day neonatal, and 19-day fetal rats for the presence of different PKC isoenzymes. Western-blot analysis of islet extracts showedthe presence of PKC isoforms in both adult and neonatal tissues. Immunocytochemistry of adult islets revealed a differential expression in islet cell types. PKC-α was found only in β-cells, PKC-γ in α-cells, and PKC-ε in δ-cells and vascular walls. Immunoreactivity for PKC-β was not detected in any cell type. All three isoenzymes were also present in neonatal islets; however, in contrast to adult tissue, immunoreactivity for either PKC-α or PKC-γ was present inrelatively few cells. There was no apparent immunoreactivity for PKC-α or PKC-γ in fetal islets, although these tissues contained strong staining for insulin and glucagon. These data show that three of the PKC isoforms are restricted to a particular islet cell type, where they may play a unique role in the secretion of a specific hormone. Moreover, our results demonstrate that these enzymes, especially PKC-γ, appearduring the early neonatal period. This age-dependent expression may be linked to the development of the biphasic insulin release response.