Log Concentration Response Curve To Carbachol

Log concentration-response curve to carbachol in the absence or presence of a series of concentrations of antagonist were showed on Figure 1. The log concentration-response curve has a characteristic sigmoidal shape. The addition of higher concentration of antagonist into the organ bath made the curves gradually shift to the right in a nearly parallel manner (Fig 1). The higher concentration of Atropine, the more its curve moved to the right of the graph. However, these effects of antagonist did not change the maximum response level.
Carbachol binds and activates muscarinic receptors of parasympathetic nervous system like acetylcholine’s effects thus it is listed as a cholinergic agonist. In this simulation experiment, Carbachol was used to exert contraction effect on the guinea pig ileum. In many smooth muscles counting intestinal smooth muscles, it is well known that the majority of muscarinic receptor subtypes are M2 and M3. Although the amount of M2 is much higher than M3 (Zhang et al., 1991), M3 is primarily the receptor subtype mediating the ileum’s contractile response to agonists like Carbachol (Kerr et al., 1995). This mechanism was again confirmed by Tomonori et al. (2015) that muscarinic M3 receptors mainly mediate contractions on human smooth muscles, particularly normal bladder. …show more content…
The rightward shift of the log concentration – response curves in Fig 1 represents the affinity of the used antagonist. The higher the concentration of Atropin added, the higher the dose ratio (Table 2). It also indicates stronger effects of Atropine producing on the sites of binding receptors. However, Atropine is a reversible competitive antagonist so increasing concentrations of Carbachol are able to interfere with the interaction between the antagonist and muscarinic