BRIEF POTASSIUM DEPOLARIZATION DECREASES LEVELS OF NEUROFILAMENT PROTEINS IN CNS CULTURE

Little is known about the effects of brief potassium depolarization that occurs concurrently with transient ischemia, epilepsy and head trauma. To investigate the effect of short-term depolarization on light (NF-L), middle (NF-M), and heavy (NF-H) neurofilament proteins and determine the role played by calcium in that effect, mixed septo-hippocampal cultures were exposed to 60 mM K+ for 6 min, in the presence of 0 to 11.8 mM Ca2+. Twenty-four hours later, neurofilament immunoreactivity in Western blots of depolarized cultures was decreased to 60% or less of control levels. Decreases were Ca2+-dependent, not due to cell loss, and affected both phosphorylated and nonphosphorylated proteins. The phosphorylation state of NF-M and NF-H influenced the degree of loss observed. Changes in the pattern of immunolabelling of neuritic processes were also associated with depolarization. Thus, brief potassium depolarization may contribute to cytoskeletal disruption following brain injury.