Pig Trachealis Smooth Muscle Pharmomechanical coupling uses Internal Calcium stores whilst Electromechanical coupling uses Extracellular Calcium

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Pig Trachealis Smooth Muscle Pharmomechanical coupling uses Internal Calcium stores whilst Electromechanical coupling uses Extracellular Calcium

Crystal Nguyen

School of Anatomy, Physiology and Human Biology, The University of Western Australia, WA, 6009

Introduction
Smooth muscle contraction occurs when calcium is present in the smooth muscle cell and binds onto calmodulin to activate myosin light chain kinase (Wilson et al., 2002). Phosphorylation of myosin light chains result in myosin ATPase activity thus cross-bridge cycling occurs causing the muscle to contract (Horowitz et al., 1996). There are two known models of excitation and contraction in smooth muscle, electromechanical coupling (EMC) and pharmomechanical coupling
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Next, to determine if contraction via the EMC pathway requires extracellular or intracellular calcium, the second type of stimulus was used and the tissue was stimulated using calcium free K+-depolarising solution. The bathing solution in this experiment was calcium free solution to make sure all extracellular calcium was eliminated, as without calcium, the EMC pathway is expected to produce no response.

The second experiment sought to determine whether calcium entry is via L-type calcium channels, therefore, verapamil (10-5 M) was used to block these channels. The tissue was then stimulated using 0.2ml of Ach (10-5 M) and K+-depolarising solution.
Results
When the tissue was immersed in calcium free solution and stimulated with Ach via the PMC pathway, a small contraction (1.15g) was observed compared to the baseline contraction trace (6.37g). Contraction recovered when the bathing solution was changed back to normal Krebs (5.63g). For the next stimulus, K+-depolarising solution, the baseline control produced a force of 6.17g in normal Krebs solution. When calcium free K+-depolarising solution was used to stimulate the tissue in calcium free solution, via the EMC pathway, the tissue barely contracted at 0.09g. In the second experiment, verapamil was added to the bathing solution. When the tissue was stimulated by Ach in the presence of verapamil, it

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