Inhibitory effect of Mn on the contracture of frog rectus abdominis muscle induced with local anesthetics

Abstract

Using frog rectus abdominis muscle, an inhibitory effect of MnCl2 toward the muscle contracture induced with several local anesthetics was examined. An isolated rectus muscle from Rana nigromaculata was bathed in frog-Ringer solution bubbled with 95% O2-5% CO2. The following local anesthetics (LA) were applied to the muscle and an isotonic contracture was recorded for 5 min. The concentration required for each LA to elicit a moderate shortening on recording paper was obtained. The sufficient concentration of each LA(mM) is shown in parenthesis: Procaine(40 mM), lidocaine(20 mM), mepivacaine (10 mM), T-caine(10 mM), tetracaine(5 mM), bupivacaine(2mM), dibucaine (2 mM) and caffeine (4 mM, not LA). After the sufficient contracture by each LA was recorded as above, several concentrations of MnCl2 were applied on the muscle with LA simultaneously, and the concentration of Mn for complete inhibition was estimated. The following values for the ratio of the concentration of Mn(mM) and LA(mM) which induced a complete inhibition, (Mn2+/LA), were obtained. For procaine, the ratio was (5. 8/40)=0.15; lidocaine, (6/20) = 0.3; mepivacaine, (6.9/10)=0.69; priloeaine, (5/10)=0.5; these ratios were under 1.0 and easily inhibited by lower Mn concentration than those of LA. Tetracaine had a ratio of (12/5)=2.4 and bupivacaine, (3.8/2)=1.9; they were over 1.0 and inhibited by higher Mn than those of LA. T-caine was (400/10)= 40, and this was the most resistant one to Mn-inhibition. As conclusions, although each LA had an individual different strength in concentration to elicit contractures between 2 to 40 mM, the concentration of Mn to inhibit LA contracture didn’t correspond to each concentration of LA, but the concentrations of Mn were of about the same strength from 5 to 10 mM.