Dual response of calpain to rat brain postdecapitative ischemia

Abstract

Calpains, Ca(2+)-dependent neutral proteinases (microM and mM Ca(2+)-sensitive), and their endogenous inhibitor calpastatin were examined in rat brain. Specific activity of m-calpain exceeded almost 10 times that of mu-calpain, and the both isoforms of calpain together with calpastatin were mainly located in the soluble fraction of homogenate. Acute postdecapitative ischemia of 15 min duration resulted in a gradual, time-dependent decrease of total mu-calpain activity (to 60% of control values) and in the moderate elevation of calpastatin activity (by 28%). The decrease of total mu-calpain activity coincided with its remarkable increase (above 300% of control values) in particulate fraction. In the case of m-calpain, the only observed effect of ischemia was its redistribution and, as a consequence, the elevation of activity in particulate fraction. The accumulation of breakdown products, resulting from calpain-catalyzed proteolysis of fodrin (as revealed by Western blotting) indicated activation of calpain under ischemia. The findings suggest that this rapid activation involves partial enzyme translocation toward membranes, and is followed (at least in acute phase) by mu-calpain downregulation and increased calpastatin activity.

Activity of calpain in subcellular fractions of the rat brain

“…In some pathologies, a decrease in the calpain activity in the soluble fraction and an increase in the membrane fractions obtained from rat brain tissue were observed [26]. A few authors consider binding of calcium-dependent proteinases with the membranes as a way of regulation of the activity of this proteolytic system.…”

“…Thus, investigation of the distribution of calpain at the subcellular level can refine our knowledge of the mechanisms of functioning of this enzyme, explain the reasons for a number of pathologies of the nervous system, and help in the search for methods for their corrections (there are data that intracellular localization of this enzyme changes in some pathological states) [25,26].…”

Effect of L-carnitine on postischemic inhibition of protein synthesis in the rat brain

“…Another known mechanism affecting postischemic protein synthesis mainly by degradation of initiation factors 4E and 4G is activation of calpain(s) (Neumar et al 1995(Neumar et al , 1998Zalewska et al 1998;Lipton 1999;White et al 2000;DeGracia et al 2002;Kumar et al 2003). L-carnitine, which protects rats against glutamate toxicity, also prevented MAP-2 degradation by cytosolic Ca 2+ -dependent protease, which has been identified tentatively as calpain I (Felipo et al 1993).…”

Effect of Lipids on the Activity of Calpain in Subcellular Fractions Obtained from the Rat Brain

“…Proteins of cytoskeleton, different enzymes (kinases, phosphatases, and phospholipases), and also proteins of membrane receptors and transporters [4] are substrates for the above enzymes. Calpains can be found in both cytoplasmic and membrane cellular fractions, but data on their amount and ratios in these fractions are contradictory; it seems probable that these indices in various tissues are different [5][6][7]. Calpains are involved in numerous processes that are realized in cells of the nerve tissues under normal conditions (e.g., structural and functional reorganization of synapses related to long-term potentiation of synaptic transmission and the control of neurotransmitter release) [8,9].…”