Abstract
As the concentration of external K+ was raised from 35 to 351 mM, the vas deferens previously labeled with 3H-norepinephrine (3H-NE) released increasing amounts of radioactivity into the medium in which it was bathed. Exposure of the vas deferens and seminal vesicle to high K+ for 10 minutes caused a 2-to 4-fold greater release than did an exposure of 1 minute. K+-induced release from normal vas deferens and seminal vesicle was completely blocked by calcium deprivation, lanthanum (l0-4 M) or cobalt (l0-3 M). Restoration of release was evident shortly after changing the medium to normal Krebsbicarbonate solution. Tissues obtained from reserpine-pretreated guinea pigs which were treated in vitro with monoamine Oxidase (MAO) inhibitor, and then incubated with 3H-NE, released upon field stimulation only a small amount of radioactivity compared to that released spontaneously in an equivalent time period. However, such tissues released progressively higher concentrations of radioactivity when exposed to K+ (35-351 mM). Although reserpine-pretreated and MAO-blocked vas deferens retained only one-fourth as much 3H-NE as normal tissue, the fractional release of total 3H by high K+ was almost 2-fold greater in the case of reserpine-pretreated and MAO-blocked tissues. The fractional release of 3H-NE from both types of tissues was essentially the same. In another aspect, K+-induced release of NE from normal against reserpine-pretreated and MAO-blocked tissues differed in that there was a lack of calcium requirement for K+ to release NE from reserpine-pretreated tissues. It is concluded that high K+ can release NE from extragranular sites of the sympathetic nerves of reserpine-pretreated and MAO-blocked tissues without external calcium, whereas is obligatory in the physiological release of NE.
Footnotes
- Received June 21, 1973.
- Accepted May 28, 1974.
- © 1974 by The Williams & Wilkins Co.
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