Calpain, calpastatin activities and ratios during myocardial ischemia-reperfusion.
The purpose of this study was to test the hypothesis that myocardial ischemia-reperfusion (I/R) is accompanied by an early burst in calpain activity, resulting in decreased calpastatin activity and an increased calpain/calpastatin ratio, thereby promoting increased protein release. To determine the possibility of a 'calpain burst' impacting cardiac calpastatin inhibitory activity, rat hearts were subjected (Langendorff) to either 45 or 60 min of ischemia followed by 30 min of reperfusion with and without pre-administration (s.c.) of a cysteine protease inhibitor (E-64c). Myocardial function, calpain activities (casein release assay), calpastatin inhibitory activity and release of CK, LDH, cTnI and cTnT were determined (n = 8 for all groups). No detectable changes in calpain activities were observed following I/R with and without E-64c (p > 0.05). Both I/R conditions reduced calpastatin activity (p < 0.05) while E-64c pre-treatment was without effect, implicating a non-proteolytic event underlying the calpastatin changes. A similar result was noted for calpain-calpastatin ratios and the release of all marker proteins (p < 0.05). In regard to cardiac function, E-64c resulted in transient improvements (15 min) for left ventricular developed pressure (LVDP) and rate of pressure development (p < 0.05). E-64c had no effect on end diastolic pressure (LVEDP) or coronary pressure (CP) during I/R. These findings demonstrate that restricting the putative early burst in calpain activity, suggested for I/R, by pre-treatment of rats with E-64c does not prevent downregulation of calpastatin inhibitory activity and/or protein release despite a transient improvement in cardiac function. It is concluded that increases in calpain isoform activities are not a primary feature of l/R changes, although the role of calpastatin downregulation remains to be elucidated.
Enns
D
D
School of Kinesiology, Faculty of Health Sciences, Faculty of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
Karmazyn
M
M
Mair
J
J
Lercher
A
A
Kountchev
J
J
Belcastro
A
A
D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D008297:Male; D017202:Myocardial Ischemia / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015427:Reperfusion Injury / Q000378:metabolism*
D002135:Calcium-Binding Proteins; C033668:calpastatin; D002154:Calpain