Verapamil-induced creatine kinase loss from rat slow and fast muscles.

The purpose of this study was to determine the dose-response relationship between verapamil HCl and creatine kinase (CK) release from isolated rat slow (soleus, S) and fast (flexor digitorum profundus, F) skeletal muscles. Total CK activity in F muscle was approximately 2x greater than in S muscle. For both S and F muscles, CK release as a function of verapamil concentration in the incubation medium was linear (r = 0.94); the slope of the line for F muscle was 4.5x that of the S muscle. S and F muscles lost up to 38-44% of their total CK activity during the 2 hr incubation. The CK activity lost to the medium was 100% of the MM isoform. The mechanism of the enzyme release is not known.