Key result
Muscle grafts from myotonic ADR mice retained their myotonic phenotype in wild-type hosts, whereas wild-type grafts in ADR hosts showed no myotonia, proving the defect is intrinsic to the muscle.
Muscle transplantation experiments in mice demonstrate that the myotonic ADR phenotype is an intrinsic muscle property rather than being determined by the neural or humoral environment.
Supports intrinsic muscle defect in myotonic models; leaves open translation to human disorders.
Developmental aspects of an animal model of myotonia, the mouse mutant called "arrested development of righting response" (ADR phenotype), were studied. Adult ADR muscle is characterized by a low chloride conductance of the membrane, leading to hyperexcitability, and by a low parvalbumin content. The myotonic hyperexcitability (as measured by the extent of "aftercontractions") of ADR muscle increased steeply between postnatal days 9 and 18, by which time it had approached the adult level. To study the tissue autonomy of the myotonic phenotype, muscle grafts were performed in all four combinations between ADR and wildtype (WT phenotype) donors and hosts. In most experiments, the relative contributions of donor and host to the regenerated muscles were determined by an allelic marker (glucose phosphate isomerase). In WT and ADR hosts, ADR grafts showed myotonic responses that in WT nude mouse hosts were incomplete and similar to those of juvenile ADR muscle. In no case did grafts from WT donors show any myotonia. This shows that the myotonic ADR phenotype is based on an intrinsic muscle property most likely related to the plasma membrane. The parvalbumin contents of grafted muscles, when compared with those of untransplanted muscles, indicated graft-host interaction in the expression of this secondary phenotypic property.
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Füchtbauer et al. (1988) studied Myotonia (animal model). Muscle transplantation vs. Autografts and untransplanted muscles was evaluated on Myotonic response (hyperexcitability measured by myotonic index M) and parvalbumin content. Muscle grafts from myotonic ADR mice retained their myotonic phenotype in wild-type hosts, whereas wild-type grafts in ADR hosts showed no myotonia, proving the defect is intrinsic to the muscle.
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