Rodolfo E. Hernández

Sequential determination of calcium distribution in B cells at the various phases of glucose-induced insulin secretion

SummaryLocalization and quantification of calcium pyroantimonate precipitates within the B cells, and determination of insulin secretion were performed in rat pancreas perfused with 3.3 and 16.6 mmol/l glucose. Observations were carried out during the peak, the refractory period, and at 10 and 20 min in the second phase of glucose secretion after the start of a glucose challenge. Specific calcium pyroantimonate precipitates, assessed by EGTA cross-incubation, appeared attached to plasma membrane, Golgi complex, mitochondria, cytoplasmic matrix and secretory granules. The total number of cellular calcium pyroantimonate precipitates increased with perfusion time, being significantly higher at every time-point with the higher concentration of glucose (16.6 mmol/l) than with the 3.3 mmol/l glucose concentration. Calcium pyroantimonate precipitates showed a progressive increment both in plasma membranes and mitochondria. In the cytoplasmic matrix, B granules and Golgi complex, a sharp increase in the number of precipitates was detected at the refractory period, followed by a continuous decrease until the end of the experiment. These results show that the number of calcium pyroantimonate precipitates, localized in different organelles, changes according to the functional state of B cells. They stress the importance of intracellular readily exchangeable pools as regulators of calcium availability for insulin stimulus-secretion coupling.

In Vitro Insulinogenic Effect of Two Monoamine-Oxidase Inhibitors

The stimulatory effect of two monoamine-oxidase inhibitors, nialamide and tranylcypromine, upon insulin secretion was studied using the in vitro rat slice pancreas incubation technic. It was found that these drugs stimulated insulin release in the presence of low levels of glucose. They were also able to enhance the insulin release elicited by high levels of glucose. These results would explain, at least in part, the protective role of MAOI in some types of experimental and clinical diabetes.

Ultracytochemical Nuclear Calcium Distribution in Pancreatic B Cells: Its Relation to Glucose-Stimulated Insulin Secretion

Calcium distribution in pancreatic B cells was studied, with the aid of the pyroantimonate technique, at different times of glucose-induced secretory activity in the perfused rat pancreas. Specificity of the pyroantimonate precipitates for calcium was assessed by EGTA cross-incubation. Quantitative studies for these calcium pyroantimonate precipitates were performed by a morphometric technique. Pyroantimonate precipitates within the B cell show both time and glucose dependence. At any time-point studied, in the nucleus as well as in other organelles, they were more numerous when glucose was increased in the medium from 3.3 to 16.6 mmol/l. The total number of nuclear calcium pyroantimonate precipitates rose sharply at the time corresponding to the refractory period, falling after that to almost the number found at the prestimulatory period. Otherwise, glucose significantly modifies the temporal distribution of precipitates bound to euchromatin, heterochromatin and perichromatin. These changes in nuclear calcium pyroantimonate precipitates during different periods of B cell secretory activity may indicate an active role of the cation in some nuclear regulatory function during glucose-induced release of insulin.

Theβ-receptors in the rat pancreas

Se estudió el efecto del isoproterenol (ISO) sobre la secreción de insulina in vitro. Los resultados indican que el ISO es capaz de estimular la secreción de insulina en forma similar a la glucosa en altas concentraciones.