Casein zymographic assays were performed to identify changes in
mu-calpain and
m-calpain activity in naive,
sham-injured, and injured rat cortex at 15 minutes, 3 hours, 6 hours, and 24 hours after unilateral cortical impact
brain injury. Cortical samples ipsilateral and contralateral to the site of injury were separated into cytosolic and total membrane fractions. Marked increases in
mu-calpain activity in cytosolic fractions in the ipsilateral cortex occurred as early as 15 minutes, became maximal at 6 hours, and decreased at 24 hours to levels observed at 15 minutes after injury. A similar temporal profile of cytosolic
mu-calpain activity in the contralateral cortex was observed, although the increases in the contralateral cortex were substantially lower than those in the ipsilateral cortex. Differences were also noted between cytosolic and total membrane fractions. The detection of a shift in
mu-calpain activity to the total membrane fraction first occurred at 3 hours after
traumatic brain injury and became maximal at 24 hours after
traumatic brain injury. This shift in
mu-calpain activity between the two fractions could be due to the redistribution of
mu-calpain from the cytosol to the membrane.
m-Calpain activity was detected only in cytosolic fractions.
m-Calpain activity in cytosolic fractions did not differ significantly between ipsilateral and contralateral cortices, and increased in both cortices from 15 minutes to 6 hours after injury. Relative magnitudes of
m-calpain versus
mu-calpain activity in cytosolic fractions differed at different time points after injury. These studies suggest that
traumatic brain injury can activate both
calpain isoforms and that
calpain activity is not restricted to sites of focal
contusion and cell death at the site of impact injury but may represent a more global response to injury.