Jj. Labella et al., ABSENCE OF MYOFIBRILLAR CREATINE-KINASE AND DIAPHRAGM ISOMETRIC FUNCTION DURING REPETITIVE ACTIVATION, Journal of applied physiology, 84(4), 1998, pp. 1166-1173
Creatine kinase (CK) provides ATP buffering in skeletal muscle and is
expressed as 1) cytosolic myofibrillar CK (M-CK) and 2) sarcomeric mit
ochondrial CK(ScCKmit) isoforms that differ in their subcellular local
ization. We compared the isometric contractile and fatigue properties
of I)control CK-sufficient (Ctl), 2) M-CK-deficient (M-CK[-/-]), and 3
) combined M-CK/ScCKmit-deficient null mutant (CK[-/-]) diaphragm (Dia
l to determine the effect of the absence of M-CK activity on Dia perfo
rmance in vitro. Baseline contractile properties were comparable acros
s groups except for specific force, which was similar to 16% lower in
CK[-/-] Dia compared with M-CK[-/-] and Ctl Dia. During repetitive act
ivation (40 Hz, 1/3 duty cycle), force declined in all three groups. T
his decline was significantly greater in CK[-/-] Dia compared with Ctl
and M-CK[-/-] Dia. The pattern of force decline did not differ betwee
n M-CK[-/-] and Ctl Dia. We conclude that Dia isometric muscle functio
n is not absolutely dependent on the presence of M-CK, whereas the com
plete absence of CK acutely impairs isometric force generation during
repetitive activation.