PH DEPENDENCY OF MU-CALPAIN AND M-CALPAIN ACTIVITY ASSAYED BY CASEIN ZYMOGRAPHY FOLLOWING TRAUMATIC BRAIN INJURY IN THE RAT

Studies employing casein zymographic assays analyzed the effects of va rying pH (from pH 6.8 to pH 8.0) on changes in mu-calpain and m-calpai n activity in naive, sham-injured and injured rat cortex 3 h following unilateral cortical impact injury. mu-Calpain activity following cort ical impact injury was enhanced between pH values of 7.2 and 7.8, with pH 7.5 being optimal. m-Calpain activity was readily detected only be tween pH values of 7.2 and 7.4, with pH 7.3 producing the most promine nt proteolytic activity. These observations suggest that strict contro l of pH is an important consideration in assessments of brain pH activ ation by casein zymography. Moreover, activation of different calpain isoforms, especially after traumatic brain injury, may be differential ly influenced by smaller changes ir physiological pH than previously r ecognized. (C) 1998 Published by Elsevier Science Ireland Ltd.