You are given an isolated skeletal muscle with its motor neuron intact This prep

Question

You are given an isolated skeletal muscle with its motor neuron intact This preparation is arranged so that you can make electrophysiological measurements from the nerve and the muscle as well as mechanical measurements of muscle contraction. You observe that if caffeine is added to the fluid bathing the preparation, the peak tension developed in a muscle twitch produced by stimulating he motor nerve is increased. List all the possible points at which caffeine may be exerting its effect. Caffeine is known to alter the transmembrane movement of calcium. What is(are) the possible site(s) at which caffeine is acting? High concentrations of caffeine causes an isolated muscle to contract in the absence of any activity in the motor nerve. This contraction is not blocked by nicotinic antagonists like curare. Where and how is caffeine exerting its effects?

Explanation / Answer

I don’t know if your prof just wants WHERE caffeine acts or would actually like to know HOW it would have to act at each point to increase tension. I gave both. Also, listing ALL the possible points is insane. S/he probably just wants you to list the ones you learned. S/he may want something more general or specific than this. You will have to fine tune it to fit. 1. a. Alterning ion channels and pumps on the neuron signal to increase the number of action potentials traveling down the neuron to the muscle b. Increasing transcription of acetylcholine (and presumably the number of vesicles or amount of acetyl choline per vesicle), thus increasing the amount of acetylcholine released into the synapse c. Inhibiting enzymes that degrade acetylcholine in the synapse d. Increasing transcription of acetylcholine receptors in the muscle cell so that there are more receptors to receive the acetylcholine e. Improve transport of to the T tubules f. Increase formation of T tubules g. Increase (or open more) transcription of ryanodine receptors (RYR) so more calcium is released from sarcoplasmic reticulum h. Increase the number of calcium binding sites of tropomysin so more sites are revealed to be bound by myosin heads i. Slow the disappearance of calcium from the cytoplasm so the muscle remains stimulated – close the SERCA2 receptors on sarcoplasmic reticulum 2. Could be acting on cell membrane channels for calcium. Increased calcium could be entering the cell from the exterior of the cell. Also could be acting on sarcoplasmic reticulum membranes - Entry (SERCA2 receptor) or exit (RYR receptor) of calcium from the sarcoplasmic reticulum. 3. At the receptors on the sarcoplasmic reticulum. It is likely increasing the exit of calcium from the sarcoplasmic reticulum and/or blocking calcium’s reentry into the sarcoplasmic reticulum.

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