Table 3

Dose-ratio test for competitive antagonism of local anesthetics at muscarinic receptors

Drug	DR₁ atropine	DR₂ drug	DR_{1 + 2} atropine + drug	DR₁ + DR₂ − 1 expected value for competition	DR₁DR₂ expected value for noncompetition
Quinacrine	36.0 ± 1.9	3.5 ± 0.4	81.2 ± 3.8^b	38.5 ± 2.2	128.6 ± 19.1
Chloroquine	34.2 ± 2.1	4.9 ± 0.6	52.3 ± 4.2^3-a	38.1 ± 1.7	173.3 ± 7.6
Tetracaine	30.8 ± 2.0	3.8 ± 0.2	33.8 ± 2.4^3-c	33.5 ± 2.2	116.4 ± 12.2
Procaine	34.6 ± 2.6	9.5 ± 2.0	35.1 ± 2.6^3-c	43.1 ± 1.7	315.5 ± 56.8

Drugs used were 5 × 10⁻⁶ M quinacrine, 10⁻⁵ M chloroquine, 3 × 10⁻⁵ M tetracaine, 10⁻⁴ M procaine and 10⁻⁸ M atropine. The guinea pig ileal longitudinal muscle strips were pretreated with each drug or a combination of the drugs for 30 min, and the dose-response curves for acetylcholine were examined in the presence of the drugs. Dose-ratios were determined from the parallel shift of the curves. Values are mean ± S.E.M. (n = 3–5).

↵3-a P < .05 and ^b P < .001 compared with the expected dose-ratio value for competition.
↵3-c Not significantly different from the expected dose-ratio value for competition (P > .05).