Effect of Local Anesthetics on Calcium Activated ATPase and Its Partial Reaction with Fragmented Sarcoplasmic Reticulum from Bullfrog and Rabbit Skeletal Muscle1

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Abstract
In reference to the results of Suko et al . ( Biochim. Biophys. Acta (1976) 443, 571–586), we examined if the effect of tetracaine, a local anesthetic, is identical with that of halothane, a general anesthetic, on Ca-ATPase and its partial reactions with fragmented sarcoplasmic reticulum from bullfrog (frog FSR) and rabbit skeletal muscle (rabbit FSR), revealing some effects specific to species as well as common ones. 1. Tetracaine at 1 m m decreased Ca uptake activities to about 70%. The extent of the inhibition with frog FSR was similar to that with rabbit FSR. Tetracaine (1 m m ) caused a sluggish leakage of Ca from loaded FSR, which may be due to a nonspecific increased permeability of the membrane. 2. With frog FSR, tetracaine decreased Ca-ATPase activity to about 70% of the control over the whole range of Ca 2+ concentrations without changing the EP level, whereas it increased the ATP-ADP exchange rate. These results are at variance with the results of Suko et al . 3. With rabbit FSR, tetracaine decreased Ca-ATPase activity at Ca 2+ concentrations lower than 1 μm, while it increased it at higher Ca 2+ concentrations. However, Ca-ATPase activity in the presence of 5 μ m A23187 was decreased by 1 m m tetracaine over the whole range of Ca 2+ concentrations. The level of EP decreased over the whole range of Ca 2+ concentrations with a lowered apparent affinity to Ca 2+ . The ATP-ADP exchange rate was decreased at Ca 2+ concentrations lower than 1 μ m , and increased at higher concentrations. These are consistent with the results of Suko et al . 4. Some of the effects of tetracaine can be explained consistently as follows: it shifts the equilibrium between E·ATP·Ca and EP toward E·ATP·Ca, and it decreases the rate of EP decomposition. Tetracaine contrasts with halothane, which largely affects the steps to the formation of E-ATP-Ca by reducing the affinity for Ca 2+ .

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