Cholinergic Drugs and Antagonism in Intestinal Effects: Lab Insights

PHL 313 (Lab. 2) Effect of cholinergic drugs on intestine and % of antagonism. 1

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The Muscarinic Actions -- Similar to those of parasympathetic stimulation (M1): CNS, PNS, gastric parietal cells (M2): conducting tissue (M3): exocrine glands; smooth muscle 3

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Cholinergics agonist Cholinergic agonists (direct acting ) Acetylcholine Bethanechol Pilocarpine Carbachol Anticholinesterases (indirect acting ) reversible : Neostigmine, physostigmine, pyridostigmine Irreversible : (e.g Organophosphates ) (isoflurophate, echothiophate ) 5

Cholinergic Antagonists [Anticholinergic Agents] Block the actions of acetylcholine at muscarinic or nicotinic cholinoceptors. Cholinergic antagonists competitively inhibit the activity of endogenous Ach. Antimuscarinic agents:inhibit muscarinic receptor-mediated responses. Atropine Scopolamine Ipratropium Ganglionic-blocking agents:inhibit nicotinic receptor-mediated responses at the ganglia. Hexamethonium Pentamethonium Neuromuscular-blocking agents:inhibit nicotinic receptor-mediated responses at the neuromuscular junction. 1. 2. Non-depolarizing : D-tubocurarine Depolarizing : suxamethonium 6

Depolarization 1- Resting potential: In order to maintain the cell membrane potential, cells keep a low concentration of sodium ions and high levels of potassium ions within the cell (intracellular). The sodium-potassium pump moves 3 sodium ions out and moves 2 potassium ions in, thus in total removing one positive charge carrier from the intracellular space. 2- Depolarization is a positive-going change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential. 3- Hyperpolarization is the opposite of depolarization, and inhibits the rise of an action potential. 7

Procedure:- 1- Add 0.2 ml Nicotine and record the response within 10 seconds then wash. 2- Add 0.2 ml C6 wait 2 minutes and add 0.2 ml Nicotine and record the response within 10 seconds then wash. 3- Add 0.2 ml Ach and record the response within 10 seconds then wash. 4- Add 0.2 ml atropine wait 2 minutes and add 0.2 ml Ach and record the response within 10 seconds then wash. 5- Add 0.2 ml BaCl2 and record the response within 10 seconds then wash. 6- Add 0.2 ml C6 wait 2 minutes and add 0.2 ml BaCl2 and record the response within 10 seconds then wash. 7- Add 0.2 ml atropine wait 2 minutes and add 0.2 ml BaCl2 and record the response within 10 seconds then wash. 8- Print the figures and calculate the % of antagonism with agonist (4 equations).

Effect Of Nicotine & Hexamethonium % of antagonist X1 X2 * 100 X1 X1 Wash No Wash x2 9 Hexamethonium (C6) Dil. Nicotine Dil. Nicotine

Effect Of Ach & Atropine % of antagonist X1 X2 * 100 X1 X1 Wash No Wash x2 10 Atropine Ach Ach

Effect Of Bacl2 & Atropine % of antagonist X1 X2 * 100 X1 X1 x2 x2 No Wash Wash Wash No Wash Bacl2 Atropine Hexamethonium (C6) Bacl2 11 Bacl2

Chemicals 1- Tyroid solution 2- Ach (0.01%) 3- Dilute Nicotine (0.01%) 4- Hexamethonium (C6) (0.1%) 5- Atropine (0.1%) 6- Barium Chloride (3%)