Combined myofibrillar and mitochondrial creatine kinase deficiency impairs mouse diaphragm isotonic function

Creatine kinase (CK) is an enzyme central to cellular high-energy phosphate metabolism in muscle. To characterize the physiological role of CK in respiratory muscle during dynamic contractions, we compared the force- velocity relationships, power, and work output characteristics of the diaphragm (Dia) from mice with combined myofibrillar and sarcomeric mitochondrial CK deficiency (CK[-/-]) with CK-sufficient controls (Ctl). Maximum velocity of shortening was significantly lower in CK[-/-] Dia (14.1 ± 0.9 L(o)/s, where L(o) is optimal fiber length) compared with Ctl Dia (17.5 ± 1.1 L(o)/s) (P < 0.01). Maximum power was obtained at 0.4-0.5 tetanic force in both groups; absolute maximum power (2,293 ± 138 W/m²) and work (201 ± 9 J/m²) were lower in CK[-/-] Dia compared with Ctl Dia (2,744 ± 146 W/m² and 284 ± 26 J/m², respectively) (P < 0.05). The ability of CK[-/- ] Dia to sustain shortening during repetitive isotonic activation (75 Hz, 330-ms duration repeated each second at 0.4 tetanic force load) was markedly impaired, with CK[-/-] Dia power and work declining to zero by 37 ± 4 s, compared with 61 ± 5 s in Ctl Dia. We conclude that combined myofibrillar and sarcomeric mitochondrial CK deficiency profoundly impairs Dia power and work output, underscoring the functional importance of CK during dynamic contractions in skeletal muscle.