Altered regulation of pancreatic glucagon in male rats during aging.

Using x-ray diffraction, the interaction of calcium ions with dipalmitoyl phosphatidylcholine (DPPC) multilayers in excess solution has been studied as a function of temperature over a range of concentrations. We have discovered order-disorder-order transformations as a function of both increasing temperature and calcium concentration. For pure DPPC, the pretransition is characterized by a large increase in lattice disorder. For low calcium concentrations, a similar increase in lattice distortion occurs for all temperatures. The high temperature phase is marked by a significant reduction in this disorder. Likewise ordering of the multilayer is regained at high calcium concentrations.