Parvalbumin (PV) is a soluble Ca++ binding protein which is particularly concentrated in fast muscles of rodents. We have developed a new protocol to fix frozen sections of muscle by formaldehyde vapor, which enabled us to immunochemically stain serial frozen sections for PV. Fiber types were defined on the basis of myosin ATPase stability, and of isomyosins identified by a variety of antibodies because ATPase stability alone yielded ambiguous results in the mouse. Slow Type I fibers in mouse and rat were devoid of PV and had intermediate to high SDH levels. Fast fiber subtypes IIA, IIB, and IIX-like were defined in the mouse on the basis of the similarity of their myosin heavy chain immunoreactivity to these types in the rat. The soleus muscle was usually PV negative, but a small population of strongly PV-positive IIX-like fibers was present in the mouse. In mouse fast muscle, small diameter IIA fibers were PV negative with high SDH activity. In both mouse and rat, PV reactivities of IIB and IIX fibers were higher than those of IIA and I, whereas SDH levels of IIA, IIX, and I fibers were higher than those of IIB. Thus, PV content correlated with the type of myosin ATPase but not with SDH levels. The method described for immunocytochemistry of PV may be applicable to other highly soluble proteins.

The soluble Ca(++)-binding protein parvalbumin (PV) is highly concentrated in fast muscle fibers of the wild type mouse. Employing Sandwich ELISA, we have shown that PV is present in the serum of normal mice and that its level is indicative of the disease status of muscle. Elevated PV levels were found in mice with X-linked dystrophy (mdx) and reduced levels in myotonic (ADR) mice. Serum creatine kinase (CK) levels were elevated in mdx and normal in ADR mice. Because myotonic mouse muscle has a strongly reduced PV content, the reduced PV serum level in ADR mice indicated that serum PV is derived from skeletal muscle. Serum PV in mdx mice, in which muscle PV content is close to normal, is a measure of the necrosis of fast muscle fibers. Serum levels of PV and CK were not significantly elevated in heterozygous (mdx/+) carrier females. Serum PV in Duchenne patients was below the limit of detection.

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