Elemental and water content of cultured bovine adrenal chromaffin cells and their secretory granules have been measured and compared with isolated chromaffin granules using rapid freezing, ultracryomicrotomy, x-ray microanalysis and electron energy loss spectroscopy. Changes in monovalent ion concentrations on isolation were found to be large whereas calcium and phosphorus concentrations remained approximately constant. Using measured water contents of different compartments it was possible to estimate a positive granule membrane potential (inside to outside) of approximately 10 to 16 mV. Additional experiments were performed to measure changes in granule composition by adding ammonia to the culture medium to induce changes in internal pH. Cellular water content was determined using inelastic electron scattering as measured by EELS. The method was first tested on hydrated cryosections of standards and was then applied to different compartments of the chromaffin cell.
