Table of Contents
An introduction
Process
Data Handling
Talking
Original: The meeting was adjourned
Paraphrased: The gathering was ended.
This is an introduction.
The ileum contains a circular smooth musculoskeletal layer. The smooth muscle is a muscarinic receptor for acetylcholine, which responds to acetylcholine and causes a muscle contraction (Widmaier and al., 2016). This practical aimed to investigate the effects of increasing ACh on a segment guinea-pig ileum. The EC50, which is a concertation of the agonist which produces 50% of maximal response (Rang et.al., 2016), and Emax were calculated. The concentration of ACh should correlate positively with the strength contractions of tissues.
MethodA guinea’pig was humanely executed by cervical dislocation. The ileum was mounted in a 38ml sterile organ bath by threading a short segment (1cm-1.5cm). The organ was kept at a 36degC temperature with Tyrode’s aerated solution. The segmented ileum of the ileums was attached to the end of the lever, which was connected to a isotonic-transducer. This allowed the Powerlab device to record the voltage of contractions. A 1g-weight was attached at the other end to tension the tissue. Addition Acetylcholine
ACh concentrations between 1*10-9M and 8.192*10-6M were achieved by a series of serial ACh dilutions. ACh doses were added over a period of 3 minutes. The tissue response to the lowest concentration ACh in the organ bath was measured for 30 second. Overflow was used to wash out the solution and remove ACh. Two minutes of resting the tissue allowed the temperature in the bath to reach a stable level. The concentration of ACh was increased by twofold in the organ-bath and the tissue’s responses were recorded.
Data HandlingA data graph is generated by LabChart. The voltages recorded were used to calculate Emax, and the percentage maximum response. Microsoft Excel produced a graph showing the percentage maximal response versus log[ACh(M)]. The graph was used to calculate the EC50 value.
Figure 1: A graph showing the response to increasing acetylcholine concentrations in a segment of guinea-pig ileum. Data is expressed in percentages of the maximum response measured in millivolts. The graph displays an EC50 of 3,98*10-8M.
Figure 2 shows the data trace of the different ACh levels on a segment from guinea pigs ileum. The data is measured in millivolts.
The concentration of ACh is positively correlated with the strength recorded in Figure 1. ACh did not cause tissue contractions until the threshold concentration of 4*10-6M. The contractions were similar from 4*10-9M down to 1.6*10-8M. The strength of tissue contractions increased dramatically between 1.6*10-8M – 6.4*10-8M. ACh concentrations of 2.56*10-7M produced the maximum response. As ACh concentrations increase, contractions are weaker. ACh has a pEC50 value 7.4 and a Emax value 353mv.
DiscussionThe design of the experiment has flaws. Data is subject to outliers because of the small sample. This can be fixed by repeating the test with more guinea-pigs. Results are consistent with those obtained in earlier studies. Ringdahl’s (1986) study found that the pEC50 for ACh on a guinea-pig ileum was 7.44.
The results are in line with expectations, as there is a correlation between ACh concentration and muscle contraction strength. ACh did not initially generate a reaction because it was not in a concentration high enough to bind and activate the muscarinic acetylcholine (MACH) receptor. The small increase may have been due to the receptors of some smooth muscles cells binding with sufficient ACh in order to generate an action-potential, which caused the muscle contraction. ACh at high ACh concentrations can be able to bind with receptors on most of the smooth cell, causing a large muscle response. It is possible that the receptors have become desensitized, or it could be an error in the experiment.
