BIOM2011 Cardiac function final PDF

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Warning: TT: undefined function: 32Course Code BIOMCourse Title Integrative Cell and Tissue BiologyCourse Coordinator Associate Prof. Bradley LaunikonisDue Date 10/05/Assignment Title Effect of Antagonist and Agonist on the CardiacFunction of Bufo Marinus HeartWord Count 2010Date Submitted 10 /05/Ex...

Description

Course Code

BIOM2011

Course Title

Integrative Cell and Tissue Biology

Course Coordinator

Associate Prof. Bradley Launikonis

Due Date

10/05/19

Assignment Title

Effect of Antagonist and Agonist on the Cardiac Function of Bufo Marinus Heart

Word Count

2010

Date Submitted

10/05/19

Extension applied for Yes

/ No

Revised Date N/A

Student Number

Surname

First Name

45365791

Hopkins

Denya

Effect of an Antagonist and Agonist on Cardiac Function of Bufo Marinus Heart Introduction: The sympathetic division of the autonomic nervous system plays a vital role in cardiac activity through initiation of the “flight or fight” response. This produces a variety of inotropic (increased cardiac contractility) and chronotropic effects (accelerated heart rate) and pacemaker cells play a pivotal role in regulating these effects. (Gordon et al, 2015) In amphibians, such as a frog, the heart consists of three chambers, one ventricle and two atria. Frog heart excitation is myogenic, meaning contraction occurs within the heart muscle itself. Pacemaker cells, located in the sinus venosus, are specialised cells that generate an action potential (impulse), which determines the heart rate. Due to the “leaky” nature of these cells, calcium ions enter through multiple pathways; notably an inward current through voltage dependant calcium channels (VDCCs) and a sodium-ion exchanger. During membrane depolarisation, an L-type VDCC opens and allows calcium ions to enter the cell, which results in a rise in action potential but are subsequently inactivated soon after opening. (Mangoni et al, 2006) In addition to heart rate and contractility being mediated through the action of pacemaker cells, it is also regulated by the release of two catecholamines; norepinephrine (noradrenaline) and epinephrine (adrenaline). Both catecholamines bind to specific adrenergic receptors, alpha or beta, which belong to the G-protein coupled receptor family (GCPR). Chemicals which trigger these adrenergic receptors are known as either antagonist, responsible for inhibiting receptors or agonist, known to activate receptors. Adrenaline is an agonist that binds to both Alpha and Beta adrenoreceptors. However, Propranolol is an antagonist which interacts with Beta-1 and Beta-2 receptors, through non-selective beta blocking. Beta-blockers competitively bind to and inactivate betareceptors, therefore inhibiting sympathetic stimulation of them. (Madamanchi. D, 2007) Beta-1 and Beta-2 receptors both couple through Gs-protein binding to adenylate cyclase during receptor stimulation to generate cAMP from ATP. This increase the intracellular production of cAMP which then binds to and activates proteins kinase A. This kinase phosphorylates various myocyte proteins including calcium release channels, phospholamban etc. Phosphorylation of the L-type calcium (Ca2+) channel, results in an influx of calcium during cell depolarisation, triggering greater release of calcium from the sarcoplasmic reticulum (SR). Phospholamban inhibits SR calcium ATPase and phosphorylation of this protein, removes the inhibition and increases the

sarcoplasmic calcium ATPase activity, thus increasing calcium stores and enhancing myocardial contractility and heart rate. (Ju and Allen, 1999) According to Ambadas (2012), in contrast to the human heart, toad hearts are predominantly comprised of beta-2 receptors (80%) as opposed to beta-1 receptors (20%). This has prompted studies, such as this, to use toads as test subjects and induce agonists and antagonists that specifically react to these receptors. This is consistent with Ambadas’ theory who suggests that adrenaline is present in the sympathetic nerves of toads and that beta-2 is an adrenaline receptor. (Ambadas et al, 2012) Therefore, the purpose of this investigation is to test the effect that an agonist (adrenaline) and an antagonist (propranolol), both individually and in combination, have on the heart rate and ventricular contractile force amplitude of B. Marinus toad hearts in comparison to the control (no drug). It is hypothesised that applying adrenaline will increase the heart rate and contractile force while application of propranolol will decrease both the heart rate and contractile force of the toad. It is also predicted that applying adrenaline and propranolol in combination, will increase the both parameters as well but to a lesser extent, due to the inhibitory action of propranolol.

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Method and Data Analysis: A double-pithed Bufo Marinus cane toad was used. The ventral surface of the toad was dissected, the sternum was removed and the thoracic cavity was exposed. The pericardium was cut away to reveal the heart. The heart was gently lifted out of the thoracic cavity and attached to a force transducer via a pin, which was passed through the ventricle muscle. The cotton thread, attached to the pin, was adjusted for sufficient tension. Positive, negative and earth ECG leads were connected to the toad using alligator clips attached to the muscle wall of the ventricle, right collar bone and right hindlimb respectively. Lab Chart was utilised to collect all experimental data. ECG and contractile force were measured for all conditions; control, agonist (adrenaline), antagonist (propranolol) and both the agonist and antagonist (adrenaline and propranolol) for 2 minutes each. The order of application for the experiment was as follows; control, applying 150uL Propranolol, 150uL Propranolol and Adrenaline in combination and 150uL Adrenaline. Drug administration was repeated 4 times (i.e. every 30 seconds) and frog ringer solution was continually applied prior to the application of each drug and after each condition to wash out previous drug condition and replicate internal conditions. This process was repeated the following week using another double pithed toad under the same conditions. The contractile force and heart rate values were recorded on Lab Chart and presented with means and standard error for all eight measurements of each condition. For contractile force, control values were recorded to compare against the amplitude produced for each of the drug conditions. Heart rate for all conditions was determined by counting the number of cycles on the ECG in 30 seconds and multiplying the value by two to obtain beats/minute. Data analysis was completed using Graph Prism in which unpaired t-tests using Welch’s correction were conducted to compare the difference in recorded contractile force and HR for each toad to determine whether the data could be pooled. A one-way ANOVA with Dunnett’s post-test was conducted to compare the control values for both contractile force and HR for the second set of data to each of the values for the drug conditions. Significance was found if p < 0.05.

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Results: Results were analysed using unpaired t-tests with Welch’s correction to compare the contractile force amplitude and heart rate data in each drug condition for the first and second sets of data. The outcome of the tests revealed that the two sets of data for heart rate and contractile force amplitude were statistically different (p...