Pathophysiology of muscle fiber necrosis induced by bupivacaine hydrochloride (Marcaine)

A single direct injection of a local anesthetic, 0.5% bupivacaine hydrochloride (BPVC) (Marcaine), into rat soleus and extensor digitorum longus (EDL) muscles produced massive fiber necrosis with extensive phagocytosis followed by rapid regeneration, predominantly in the soleus. Since the sarcoplasmic reticulum (SR) was functionally disturbed by BPVC administration as confirmed by an in vitro study, the sarcolemmal lysis seen in the early phase of degeneration was not assumed to simply results from direct damage to the plasma membrane caused by BPVC. The extracellular fluid containing a high concentration of calcium (Ca) ions then permeated into the sarcoplasm through the defective membrane resulting in hypercontracted myofibrils. Selective damage to the Z-line, an early sign of muscle degeneration, was shown by electron microscopy and SDS gel electrophoresis (preferential loss of a-actinin). Administration of leupeptin, a thiol protease inhibitor, proved to be ineffective in inhibiting the necrotic process, because the BPVC induced muscle fiber breakdown was probably too acute and fulminant to demonstrate the inhibitory effect upon the degenerative process. Well preserved satellite cells, peripheral nerves, and acetylcholinesterase activity, and the absence of fibrous tissue proliferation in this system may be responsible for the extremely rapid regeneration with complete muscle fiber type differentiation. Since the sequence of fiber breakdown induced by BPVC administration was similar to that of progressive muscular dystrophy, this chemical will be one of the most useful tools for studying the pathophysiology of fiber necrosis and regeneration in diseased muscle.