The influence of barbiturate drugs on tetraethylammonium induced contractures of the chick biventer cervicis muscle in vitro

Abstract

1. 1. Methohexitone sodium (METHO) 8.8 × 10 −5 M markedly potentiates tetraethylammonium (TEA)-induced contractures of the chick biventer cervicis muscle in vitro, (Elliott, 1979). 2. 2. A group of barbiturates were compared with METHO for their ability to potentiate TEA induced contractures. 3. 3. The concentrations of TEA which produced a 50% maximum contracture (EC 50) in the presence of METHO (8.8 × 10 −5 M and in the optimum potentiating concentrations of the other barbiturates were determined. 4. 4. The EC 50 ratios (= EC 50 METHO/EC 50 test drug) were: barbitone sodium 0.25, phenobarbitone sodium, 0.20, pentobarbitone sodium 0.90, thiopentone sodium, 2.43. 5. 5. The concentrations of the barbiturates used were: barbitone 3.1 × 10 −2 M, phenobarbitone 3.15 × 10 −3 M, pentobarbitone 6.04 × 10 −4 M, thiopentone 1.89 × 10 −4 M. 6. 6. The EC 50 ratios were adjusted by dividing by the ratio [test barbiturate]/[METHO]. 7. 7. The adjusted ratios gave the following potencies (METHO = 1), barbitone 7.13 × 10 −4, n = 6, phenobarbitone 5.58 × 10 −3, n = 8, pentobarbitone 1.33 × 10 −1, n = 6, thiopentone 1.13, n = 6. 8. 8. The potencies correlate well with the partition coefficients of the barbiturates between cell membranes and buffer ( P m/b). 9. 9. The regression y = 1.49 x - 3.12, where y = log (adjusted ratio) and x = log ( P m/ b) fits data with a correlation coefficient of 0.99.