Parvalbumin in cross-reinnervated and denervated muscles.

The extensor digitorum longus (EDL) muscle was cross-reinnervated by the soleus (SOL) nerve, leading to the well-known transformation toward a slow muscle. Nine weeks after the operation, the quantitative analysis of the Ca2+-binding protein, parvalbumin (PV), using high-performance liquid chromatography, showed a threefold reduction of PV in the cross-reinnervated EDL muscle. Denervation of the EDL muscle, which leads to an increase of the half-relaxation time, resulted in a 20% decrease of the PV concentration within 4 days. This significant lower PV level was detectable prior to any change of the myofibrillar adenosine triphosphatase (ATPase). Normal PV concentrations were reached after 9 weeks following self-reinnervation of the EDL muscle. The experiments support the view that PV is involved in the relaxation of rat fast skeletal muscles and that its expression is dependent on nerve-muscle interaction. Since PV changes preceded histochemical changes after denervation, this protein may be a sensitive marker for early stages of neuromuscular disturbances.