NSF Award
8701511
Although there is considerable indirect evidence that depolarization of nerve cell terminals leads to the entry of Ca+2 and the consequent secretion of neurohormones and neurotransmitters, the details of how ionic currents control the release of neuro-active substances from nerve terminals remain undetermined. This study by Dr. Lemos presents two preparations in which these questions can be directly addressed. Much is already known about neurohormone release from both the rat neural lobe and crab sinus gland, and the electrical activity of individual terminals has been well characterized. The aim of this research is to analyze, at the level of membrane and molecular mechanisms, how depolarization of these nerve endings causes release of their peptide neurohormones. It is now possible to prepare isolated nerve endings from both the neural lobe and sinus gland, which respond to depolarization by releasing peptide neurohormones via exocytosis. When permeabilized with detergents, thus permitting the entry of specific probes into the nerve terminals, this preparation allows insight into the cytoplasmic events leading to hormone release. These neurosecretosomes readily form seals with fire polished electrodes, making feasible the application of patch-clamp techniques to characterize the ionic currents from both the terminal membrane and intracellular organelles, such as neurosecretory granules. Finally, membrane capacitance measurements can be utilized in these preparations to directly determine the relationship between ionic channel activity and secretion at the level of the nerve terminal. These preparations, therefore, have all the properties necessary to analyze in detail the process of stimulus-secretion coupling. Elucidation of these mechanisms will represent a major advance in our understanding of how neuronal activity is controlled.
