Characterization of the calcium-induced disruption of neurofilaments in rat peripheral nerve.

Transverse frozen sections of desheathed rat peripheral nerve were incubated in media of different composition prior to fixation and processing for electron microscopic examination. Neurofilaments remained intact when these tissues were incubated in calcium-free media. A loss of neurofilaments and their replacement by granular debris occurred in myelinated and unmyelinated fibers following incubation in media containing 2 mM calcium. The calcium-mediated disruption of neurofilaments was inhibited by preincubation or incubation with 1 mM p-chloromercuribenzoate (PCMB). The inhibition by preincubation with PCMB could be partially reversed by subsequent preincubation with 10 mM dithioerythritol (DTE). Calcium-mediated breakdown of neurofilaments did not occur after prolonged preincubation in calcium-free media, a finding which suggested that neurofilament disruption was dependent upon a tissue factor which could be lost or inactivated in frozen-sectioned nerve tissues. The findings of the present study provide morphological evidence that neurofilament disruption in mammalian peripheral nerve is mediated by a calcium-activated, PCMB-sensitive enzyme in the axoplasm of myelinated and unmyelinated nerve fibers.