Potassium‐Efflux and the Response to Carbachol, Phenylephrine, Adrenaline, Noradrenaline, and Isoprenaline in Rabbit Antrum Muscle

: Longitudinal strips from the antrum of rabbit stomachs were incubated for one hour in radioactive (42K) Krebs solution, and transferred to a constant flow apparatus where they were washed with non- radioactive solution. After an equilibration period of 28 min., the strips were exposed to 10−5 M carbachol, or 10-4 M phenylephrine, noradrenaline, adrenaline, or isoprenaline. Some carbacholtreated strips were later also exposed to the adrenergic drugs. The mechanical responses and the effect of the drugs on 42K-efflux were studied. Carbachol which initiated rhythmic contractions or gave a “fused” (tetanic) contraction, produced a transient, statistically significant increase in K-efflux as compared with untreated controls. Phenylephrine, noradrenaline, and adrenaline which had no effect or initiated rhythmic contractions in inactive strips, reduced the mechanical activity in strips previously exposed to carbachol. Isoprenaline had only inhibitory effects. All the four adrenergic drugs increased K-efflux significantly in inactive strips, probably due to a-receptor stimulation, since the effect of isoprenaline could be blocked by phentolamine. Noradrenaline also increased K-efflux significantly in strips exposed to carbachol. The increase in K-efflux produced by phenylephrine in the antrum strips was not as great as that previously recorded in fundus strips. The K-uptake was the same, but K-efflux was greater than in the fundus. It is concluded that a-receptor stimulation increases K-efflux regardless of whether the mechanical response is excitatory, inhibitory, or nil.