The effect of potassium on the longitudinal muscle-myenteric plexus (LM-MP) preparation from guinea-pig was studied. The strips were exposed to elevated K+ (30 m M, 60 m M, 90 m M, 120 m M or 150 m M). A phasic contraction of the LM-MP was caused by 10m M K+ or 15 m M K+ followed by an increase of the contractile activity probably due to the increase in acetylcholine release. A higher molarity of K+ produces more marked depolarization in the LM-MP and above 22m M K+ tetanizing effects were observed. We attempted to demonstrate that opiate-like material could be released when the tissue was exposed to more than 30 m M K+ even though several different neurotransmitters could be liberated by elevated K+ molarities.

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