EXTERNAL CALCIUM-DEPENDENCE OF EXTENSOR DIGITORUM LONGUS MUSCLE CONTRACTILITY DURING BUPIVACAINE-INDUCED REGENERATION

The effect of the intramuscular injection of bupivacaine hydrochloride on selected morphological characteristics and contractile properties of adult rat extensor digitorum longus muscle was studied. Recovery of normal fiber size was already present 30 days after bupivacaine injec tion and at 90 days after injection, values of the normalized twitch t ension (mN/mg of tissue) and of the fatigue index approached those mea sured in control muscle, whereas the normalized tetanic tension remain ed 57% of control. At 7-30 days postinjection, twitch force was decrea sed by reducing [Ca2+](0) (substituted by Mg2+) or adding Co2+ (5 mmol /L(-1)). By contrast potentiation of the twitch was recorded in the pr esence of Cd2+ (2 mmol/L(-1)). Glycerol treatment only reduced, but di d not eliminate twitches developed by muscles 7 days after injection. Present results emphasize the importance of the recovery process In th e loss of the susceptibility of the contractile responses to extracell ular calcium in muscles. These data may be of interest in the evaluati on of functional aspects of muscles in which injections of viral vecto r or autologous myoblasts have been performed. (C) 1996 John Wiley & S ons, Inc.