Phosphorylative neuromodulation of the regulatory subunit of cyclic AMP-dependent protein kinase type II in skeletal muscle.

The phosphorylative neuromodulation of the regulatory subunit of protein kinase type II (R-II) in cytosolic fractions from denervated and sham-operated, contralateral soleus muscles of the rat was evaluated. The denervation-induced increase in the 32P-phosphorylation of R-II is not related to an increased dephosphorylation by cation-dependent or cation-independent protein phosphatases in the cytosolic fractions. The level of 32P-phosphorylation of an exogenous heptapeptide substrate (Kemptide) by dissociated catalytic subunits of cyclic AMP-dependent protein kinase in cytosolic fractions from denervated and sham-operated solei did not differ. Also, no change in the concentration of cytosolic R-II assessed by competitive enzyme-linked immunosorbent assays (ELISA) was found after denervation. However, the in vitro 32P-phosphorylation of R-II in these samples was increased. Taken together, our results suggest that the increased availability of autophosphorylatable sites reflects an in vivo modulation of R-II phosphorylation rather than a significant change in total R-II content.