[Abnormal secretory response to verapamil of pancreatic B cells of neonatal rats maintained in high glucose].

The effect of verapamil on insulin secretion in the presence of IBMX was studied in B cells in pancreatic monolayer cultures of the neonatal rat using a perifusion system. For the initial three days, B cells were exposed to a medium of either 5.5 or 11.1 mM glucose and 10 microM iodoacetic acid (IAA) after which they were exposed to a medium of either 5.5 or 11.1mM glucose until day 7. Insulin secretion of B cells in medium of 5.5mM glucose (day 7) was not affected by IBMX, and the observations showed that verapamil significantly suppressed the secretion of insulin. However, the second phase of secretion was significantly increased by verapamil and IBMX. In contrast, insulin secretion of B cells exposed to a medium of 11.1mM glucose (day 7) showed similar trends, but the second phase secretion was increased further by verapamil in the presence of IBMX. The total amount of secretion was 2.3 times (125.5ng/ml) the secretion of cells exposed to low concentration of glucose (day 7). These results show that there is a possibility that in the presence of IBMX, verapamil, which is known to be a Ca2+ channel antagonist, shows the action of a Ca2+ channel agonist and promotes the secretion of insulin. Moreover, there were indications that a high concentration of glucose in culture affects functional maturation and functional differentiation of pancreatic B cells of neonatal rats and impairs the intra-cellular signal transduction system.