Logothetis_post

Logothetis_post - G protein signaling pathway - Background...

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Unformatted text preview: G protein signaling pathway - Background - A muscle cell response Muscle cell response (contract or not) depends on an action potential, which in turn depends on depolarization. - change in membrane potential The plasma membrane of most cells has a resting potential around -70 to -80 mV due mainly to the Na+/K+ ATPase and K+ leak channels: Na+ high outside. When Na+ channels open, Na+ Fows IN and membrane depolarizes K+ high inside, When K+ channels open, K+ Fows OUT and membrane hyperpolarizes Resting Potential Action Potential How can an acetylcholine (ACh) signal from a nerve cell lead to a muscle cell response? G protein signaling pathway - Background - Acetylcholine receptors Two kinds of muscle ACh receptors lead to different responses (MBOC 15-9) 1. ACh stimulates Nicotinic acetylcholine receptors on skeletal muscle to cause skeletal muscle contraction Nicotinic receptor is a Na+ ion channel receptor Binding of ACh changes conformation of receptor opens receptor-gated Na+ channels and causes DEPOLARIZATION of the plasma membrane. When membrane depolarizes to -40 mV, voltage-gated Na+ channels open allowing for rapid inFux of Na+ and formation of the action potential and a contraction. 2. ACh stimulates Muscarinic acetylcholine receptors in the cardiac sinoatrial node (pacemaker that initiates the electrical impulse for ea. heart beat) to slow the heartbeat and inhibit contraction. trimeric G-protein-linked receptor that leads to activation of a K+ channel (G-protein-mediated mechanism discussed in paper) Remember K+ channel has opposite effect of Na+ channel and, thus, HYPERPOLARIZES plasma membrane G protein signaling pathway - Background - Acetylcholine receptors Two kinds of muscle ACh receptors lead to different responses Sinoatrial node (pacemaker that initiates the electrical impulse for each heart beat) rhythmic impulses generated by ordered opening and closing of different ion channels Na+ channels depolarize membrane to a threshold that triggers opening of voltage gated Ca++ channels in the plasma membrane. Rapid inFux of Ca++ generates the electrical impulse that sends an electrical impulse to the heart and causes contraction. Subsequent opening of K+ channels hyperpolarizes the membrane. Next heart beat is initiated by opening of Na+ channels....
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Logothetis_post - G protein signaling pathway - Background...

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