Muscarinic acetylcholine receptors in the XXXX ciliary body smooth muscle: spare receptors and threshold phenomenon.

@entity95 @entity2134 @entity5333 @entity5592 @entity3897 @entity5402 @entity6327
Interactions of several muscarinic drugs with their receptors were studied in the ciliary body smooth muscles of the @entity95 . The ciliary body smooth muscles responded to @entity5402 , a muscarinic full agonist, with concentration-dependent contractions, and the pD2 value of @entity5402 was 5.16 +/- 0.05. @entity3897 , a competitive antagonist of muscarinic receptors, produced a parallel shift to the right in the concentration-response curves for @entity5402 . @entity2134 which is a well-known partial agonist on muscarinic receptors in most smooth muscles did not cause any contraction in this tissue. The drug, however, behaved as a competitive antagonist on the muscarinic receptors in the ciliary body smooth muscles. The pA2 values of @entity3897 and @entity2134 versus @entity5402 obtained from the Schild plot are 8.97 +/- 0.25 and 5.17 +/- 0.09, respectively. On the other hand, @entity6327 and @entity5592 acted as a partial agonist in this tissue. The intrinsic activity, and pD2 and pA2 values were 0.41 +/- 0.02, 4.93 +/- 0.05 and 5.32 +/- 0.05 for @entity6327 respectively, and were 0.26 +/- 0.02, 5.64 +/- 0.08 and 6.12 +/- 0.16 for @entity5592 , respectively. The pA2 values of these drugs were significantly larger than the corresponding pD2 values of the drugs. The values of the negative log molar dissociation constant of @entity5402 , @entity6327 and @entity5592 estimated by the method of partial irreversible blockade of spare receptors with 3 X 10(-6) M @entity5333 were 4.53 +/- 0.08, 5.20 +/- 0.09 and 6.02 +/- 0.06, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
