Paraspinal Muscle Contractile Function Is Impaired In The Ent1-Deficient Mouse Model Of Progressive Spine Pathology

Study Design. Basic science study of the relationship between spine pathology and the contractile ability of the surrounding muscles.Objective. The aim of this study was to investigate single muscle fiber contractile function in a model of progressive spine mineralization (ENT1(-/-) mice).Summary of Background Data. Altered muscle structure and function have been associated with various spine pathologies; however, studies to date have provided limited insight into the fundamental ability of spine muscles to actively contract and generate force, and how this may change in response to spine pathology.Methods. Experiments were performed on two groups (ENT1(-/-) [KO] and ENT1(+/+) [WT]) of mice at 8 months of age (n = 12 mice/group). Single muscle fibers were isolated from lumbar multifidus and erector spinae, as well as tibialis anterior (a non-spine-related control) and tested to determine their active contractile characteristics.Results. The multifidus demonstrated decreases in specific force (type IIax fibers: 36% decrease; type IIb fibers: 29% decrease), active modulus (type IIax: 35% decrease; type IIb: 30% decrease), and unloaded shortening velocity (V-o) (type IIax: 31% decrease) in the ENT1(-/-) group when compared to WT controls. The erector spinae specific force was reduced in the ENT1(-/-) mice when compared to WT (type IIax: 29% decrease), but active modulus and V-o were unchanged. There were no differences in any of the active contractile properties of the lower limb TA muscle, validating that impairments observed in the spine muscles were specific to the underlying spine pathology and not the global loss of ENT1.Conclusion. These results provide the first direct evidence of cellular level impairments in the active contractile force generating properties of spine muscles in response to chronic spine pathology.