Differential effects of potassium on the potency of different opiods in the mouse vas deferens
In the rat vas deferens, the maximal response to acetylcholine increased almost linearly as a function of external potassium concentration, [K+]0. The magnitudes of the maximal responses in 10, 15 and 20 mM [K+]0 were 128, 155 and 184% of the maximal response in 6 mM [K+]0, respectively. The response to carbachol also increased in 20 mM [K+]0 to almost the same extent. The enhancement of the norepinephrine response was observed only in 20 mM [K+]0; its magnitude was only 125%. The increase in [K+]0 from 6 to 20 mM did not affect the sensitivity (expressed as the geometric mean ED50) either to norepinephrine or to acetylcholine. Denervation of the postganglionic nerves to the vas deferens did not affect the enhancement of the maximal responses in 20 mM [K+]0, indicating that the release of neuronal transmitters may not be involved.