Figure 1 shows that the response of the tissue increased with bath concentration of ACh (M). The logarithms of bath concentration for each response were used to form a clear sigmoidal formation, and thus depict a more clear relationship between concentration and response. Figure 1 shows the increasing rate of response as bath concentration increased, before plateauing around the highest concentrations. Responses ranged from 0.685-100%, while bath concentrations of ACh ranged from 2 x 10-10 M to 8 x 10-6 M (see Appendix, Table 1). The effective concentration causing half of the maximal response (EC50) occurred at a bath concentration of 2.74 x 10-8 M.
The Hill coefficient of this curve was 1.237, indicating positive cooperativity. A representation of the isotonic contractions of the ileum can be seen in Appendix, Figures 1 and 2. Figure 2 illustrates the response of the Guinea Pig ileum through isotonic contractions when a dose of ACh is added into the organ bath with a competitive antagonist. A relationship between response and bath concentration can be identified through the clear sigmoidal formation observed in Figure 2. The responses ranged from 0-100% while bath concentrations ranged from 2 x 10-10 M to 8 x 10-6 M (see Appendix, Table 1). The Hill coefficient of the curve was found to be 2.468 while the EC50 occurred at a bath concentration of 6.43 x 10-7.
(Legend) Figure 1. The concentration-response curve to ACh in the absence of a competitive antagonist. Each dose of ACh was added to an organ bath containing a section of Guinea Pig ileum and Tyrode’s solution at physiological temperature. The response to ACh was measured by the isotonic contractions of the ileum until the maximum response was reached for the dose, using an isotonic force transducer with metal counter-weight of approximately 0.5g. A wash cycle of approximately 30 seconds overflow was then used to prepare the tissue for the next dose.
Figure 2. The concentration-response curve to ACh in combination with a competitive antagonist (Atropine). Each dose of ACh was added to an organ bath containing a Guinea Pig ileum in Atropine solution set at bodily temperature. The response to eat dose of ACh was measured through isotonic contractions of the ileum using an isotonic force transducer with a metal counter-weight of 0.5g. The response was measured periodically until the maximum response for the dose was achieved.