Figure 3.

The effect of cAMP on the mechanical responses of permeabilized ABRM during activation at high (pCa 5) and intermediate concentrations (pCa 6) of calcium. Different muscle strips were used for each treatment. (A) Muscle was activated in pCa 5 and then 100 μM cAMP was added and the muscle was frozen. γ³²P-ATP was included from 1.5 min in activating solution on. Also shown is Coomassie blue-stained 4% acrylamide gel (lane 1) and corresponding PhosphorImage (lane 2) prepared from frozen muscle. (B) Same protocol as in A except that this muscle was activated in pCa 6. (C) Same protocol as in B except that bathing media for this muscle included peptide inhibitor (10 μg/ml) of protein kinase A. (D) 4–20% gradient gel and corresponding PhosphorImage. Lane 1, from control muscle frozen 10 min after activation in pCa 6; lane 2, from muscle activated in pCa 6 for 10 min and treated with cAMP for 3 min; and lane 3, from muscle treated as in B but in presence of peptide inhibitor of protein kinase A. MHC, myosin heavy chain. → shows the position of the CR protein.