Calcium‐dependent Alterations of Neurofilament Proteins of Rat Peripheral Nerve

Segments of rat peripheral nerve were excised and incubated in vitro under conditions which hasten or retard the penetration of calcium into tissues. The nerve segments were then homogenized in 1%SDS, 8 M‐urea and 50mM‐dithioerythritol and the extracted proteins were analyzed by SDS polyacrylamide disc gel electrophoresis. Representative samples were also fixed and processed for electron microscopic examinations. Incubational conditions which favored the penetration of calcium into the tissues caused widespread granular disruption of neurofilaments as well as the selective loss of 200,000, 150,000 and 69,000 MW proteins from the nerve segments. These structural and chemical changes occurred in the 24‐48 h interval during incubation at 37oC under nutrient conditions, but were accelerated under energy‐deprived conditions and with high‐calcium media. The same changes occurred in nerve segments incubated for 2h in media containing calcium with Triton X‐100 detergent or A23187 ionophore and in nerve segments freeze‐thawed in 0.5 mM‐calcium. These changes did not occur after parallel incubations in calcium‐free media. These findings support the view that 200,000, 150,000 and 69,000 MW proteins are components of neurofilaments and that they are susceptible to a calcium‐induced disruption.