Enhancement and Depression of Neuromuscular Transmission by Intra-arterial Injection of Potassium Chloride in the Dog

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Abstract
Tension recordings of both triceps surae were made in 9 dogs stimulated through the sciatic nerve during Na barbital anaesthesia. The effects of intra-arterial injection of KC1 on neuromuscular transmission were studied by observing the changes of tension in the perfused muscle as compared with the tension in the contralateral muscle, simultaneously stimulated. Continuous slow injn. of KC1 (2-3 mg./sec. of 1.12% soln.) produced initial enhancement and subsequent depression of neuromuscular transmission in muscle stimulated indirectly at 275 to 300 shocks/sec. Fast injn. of KC1 (15 mg./sec. of 4.2% soln.) produced a prompt depression of neuromuscular transmission. Continued fast injn. produced marked contracture and complete neuromuscular block. Enhancement of neuromuscular transmission may occur in the absence of contracture or in the presence of mild contracture. Amts. of K sufficient to induce marked contracture usually produced complete neuromuscular block. During complete neuromuscular block by KC1 injn., the response of the muscle to direct stimulation was unimpaired.