Study of changes of neuronal membrane functions with aging by tissue culture method

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The effects of a hypotonic solution on morphology and electrophysiological functions in cultured dissociated neurons can be precisely studied. From the analysis of video pictures from Nomarski optics, diameters of the cells were seen to increase and then recover to the initial values after the application of a hypotonic solution. The rate of increase of cell size in fetal neurons was 4-5 times faster. than in mature neurons. This transient depolarization and decrease of the resistance corresponded to morphological changes. However, the amplitude of an action potential scarcely changed during the cell membrane expansion. It is plausible that increased membrane tension caused by the membrane expansion might facilitate the opening of the channel. The cell membrane expansion might also increase ionic permeability through the membrane.This may reduce a swollen cell volume to the initial one by diluting the intracellular solute concentration. After this adaptation the cultured neurons were a … More ble to survive for a long time and extend process in the hypotonic environment.Cell membrane elasticity has been measured in erythrocytes by the method of Elastic Area Compressibility Modulus(EACK). A dissociated neuron is aspirated by a negative pressure into a siliconized capillary, the diameter of which is about a half that of the neuron. Cell surface area can be calculated from pictures of the aspirated neuron on a TV monitor screen. Dorsal root ganglion neurons from fetal and 3-month-old mice were dissociated and their values of the area compressibility modulus (K) were measured. The K value of adult mouse neurons was 21.3<plus-minus>10.3 dyn/cm which is about 1/10 that of erythrocytes. The K value of fetal mouse DRG neurons was 2.8<plus-minus>0.5 dyn/cm. The cell membrane elasticity decreases with aging. Since neuronal cell membrane functions closely relate to intracellular cytoskeltal filaments, elasticity of the membrane may be affected by disruption of the filaments. When 10 muM cytochalasin D was treated to adult cultured neurons, the elasticity scarcely changed. However, when 10 muM colchicine was applied to the neurons, the K value decreased to 7.80 dyn/cm. This result suggests that intracellular microtubules in a neuron may mechanically bind to the cell membrThese results suggest that a neuronal membrane becomes rigid with aging and this rigidity might cause a capability of neurite regeneration to decrease with aging. Less