title: Age-dependent decrease of the passive Rb+ and K+ permeability of the nerve cell membranes in rat brain cortex as revealed by in vivo measurement of the Rb+ discrimination ratio.
abstract: Young, adult and old male CFY rats (2, 12 and 24 mth of age, respectively) were treated with a daily dose of 30 mg RbCl/100 g body weight, in form of aqueous solution injected intraperitoneally for 14 days. A considerable part of the intracellular K+-content of the body was replaced by Rb+ during this treatment. After cessation of the RbCl injections, a relative steady state came into being in each age group, called Rb+-release period. During this period Rb+ and K+ contents of the blood serum and the cisternal CSF were measured by atomic absorption spectrophotometry, and of the intracellular space of brain cortical cells by energy-dispersive X-ray microanalysis. Ultrastructural features of the brain cortex were also checked by transmission electron microscopy. For X-ray microanalysis, the L-line of Rb at 1.694 keV energy was used at 10 kV accelerating voltage in a scanning electron microscope equipped with an EDAX System F. Rb+ and K+ concentrations were obtained for the cellular dry mass and converted into wet concentrations on the basis of intracellular water contents known from former experiments. Rb+-replacement of K+ did not cause any ultrastructural alteration in the brain cortex. However, the Rb+ accumulation displayed a very significant age-dependent increase: at the beginning of release, adult and old rats had 32.6 and 44.7 mM Rb+ in their intracellular water as against the 8.6 mM found in the young group, and similar proportional difference persisted during 20 days of the release. Rb+ discrimination ratios (DR) calculated either for the blood or the CSF displayed very considerable age-dependent increase: the values of the adult and old groups were 191 and 242% of the young one, indicating that the passive Rb+ (and K+) permeability of the nerve cell membrane decreases throughout the life span of rats. These results give further support to the membrane hypothesis of aging.
mesh_terms: D000375:Aging; D000818:Animals; D002463:Cell Membrane Permeability; D002540:Cerebral Cortex / Q000502:physiology* / Q000648:ultrastructure; D002555:Cerebrospinal Fluid / Q000032:analysis; D004577:Electron Probe Microanalysis; D008297:Male; D008564:Membrane Potentials; D008854:Microscopy, Electron; D009474:Neurons / Q000032:analysis / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000032:analysis / Q000378:metabolism*; D013054:Spectrophotometry, Atomic
chemical_list: D012413:Rubidium; D011188:Potassium