The Effect of Varying External K+ and Ca++ on the Increase in 42K‐efflux Produced by Phenylephrine and Carbachol in Circular Rabbit Fundus Strips

: Circular strips from the fundus of rabbit stomachs were incubated for one hour in radioactive (42K) modified Krebs solution. They were then transferred to a constant flow apparatus, where they were washed with inactive Krebs solutions with K+‐concentration ([K+]o) of zero, 5.9 (standard), 23.6, and 94.4 mM, and with Ca++‐free solution (0[Ca++]o). After an initial equilibration period of 32 min., the strips were exposed to 10−4W M phenylephrine or carbachol. The 42K‐efflux, the effects of the two drugs on 42K‐efflux, and the mechanical responses were studied. The 42K‐efflux was lowest at 5.9 mM K+, and highest at 94.4. Both phenylephrine and carbachol increased efflux at [K+]o of zero and 5.9 mM, and at 0[Ca++]o. Carbachol also increased efflux at [K+]o of 23.6 mM. Mechanical responses to both drugs were obtained at all [K+], and at 0[Ca++]o. Both the mechanical responses and the alterations in efflux were greatest at 5.9 mM K+, but otherwise no correlation was found between the magnitude of these two types of responses. As the incubation medium had been modified correspondingly to the washing fluid, the K‐uptake at the various [K+]o and at 0[Ca++]o could also be determined. The K+‐uptake at 0[Ca++]o was 49.3 mM K+/kg dry weight, at 0[K+]o 64.9 mM/kg, at standard [K+]o 145.2 mM/kg, at 23.6 mM K+ 176.9 mM/kg, and at 94.4 K+ it was 890.1 mM/kg. The uptake at standard [K+]o, was lower after cold storage for two days than after one day, but the length of storage did not appear to influence 42K‐efflux or the responses to phenylephrine and carbachol.