Evidence for multiple prejunctional receptor sites in XXXX isolated anococcygeus muscle.

@entity1169 @entity1766 @entity3160 @entity3858 @entity935 @entity5521 @entity1617 @entity3897 @entity112 @entity35 @entity750
In @entity35 isolated anococcygeus muscle, @entity935 (2.6 x 10(-11) M to 8.3 x 10(-10) M) produced a concentration-dependent inhibitory effect on field stimulated contractions. The effect of @entity935 was blocked by @entity1766 (2.2 x 10(-8) M) but not by @entity3160 (2.6 x 10(-10) M) or @entity1169 (1.0 x 10(-7) M), suggesting a specific prejunctional inhibitory effect. Higher concentrations of @entity935 (1.4 x 10(-7) M to 1.4 x 10(-4) M) elicited concentration-dependent contractions which were blocked competitively with higher concentrations of @entity1766 (2.2 x 10(-7) M to 1.4 x 10(-4) M) and 2.2 x 10(-6) M), suggesting a postjunctional activity. @entity1617 in very low concentrations (2.8 x 10(-11) M to 4.4 x 10(-10) M) blocked the field stimulated contractions. @entity3897 (2.6 x 10(-9) M) per se augmented them and also antagonized the inhibitory effects of @entity1617 , suggesting a prejunctional activity of @entity1617 . Higher concentrations of @entity1617 (5.5 x 10(-7) M to 7.0 x 10(-5) M) produced contractions which were not altered by @entity3897 in a concentration (2.6 x 10(-9) M) which antagonized the prejunctional activity of @entity1617 . @entity112 , in a wide range (3.1 x 10(-12) M to 2.6 x 10(-8) M), did not modify field stimulated contractions. Very low concentrations of @entity750 (1.2 x 10(-11) M to 3.8 x 10(-10) M) had an inhibitory effect on field stimulated contractions. @entity3858 (2.8 x 10(-9) M) enhanced the responses to electrical stimulation and antagonized the @entity750 -induced inhibitory effect. Still higher concentrations of @entity750 (1.9 x 10(-6) M to 1.0 x 10(-3) M) produced concentration-dependent contractions. @entity3858 (8.5 x 10(-7) M) failed to antagonize, whereas @entity5521 (1.0 x 10(-6) M) antagonized @entity750 competitively. @entity935 (8.3 x 10(-10) M), @entity1617 (4.4 x 10(-10) M) or @entity750 (3.9 x 10(-10) M), in concentrations which produced a maximal prejunctional inhibitory effect, did not alter the EC50 value of NA, ruling out a post-junctional effect. Moreover, the concentration ratios of these agents for EC50 pre to EC50 post were less than 1, suggesting their preferential prejunctional site of action. It is concluded that multiple prejunctional site of action. It is concluded that multiple prejunctional receptor activities for DA, @entity1617 (muscarinic) and @entity750 , which modify the release of neurotransmitter, may be operative in this preparation.
