Step I muscle, Ca & contraction...

[peter90036]

is there very little/no free Ca2+ inside the muscle cell cytoplasm - at rest ?
as i understand if Ca is available it will lead to contraction?

 

[EMCC]

is there very little/no free Ca2+ inside the muscle cell cytoplasm - at rest ?
as i understand if Ca is available it will lead to contraction?

There is very little "free floating calcium" in the cytoplasm at rest. When an action potential (electrical impulse), however, comes at the cell, the Sarcoplasmic Reticulum dumps a whole bunch of calcium into the cytoplasm to bind to Calmodulin et. al to cause contraction. When the impulse stops, the calcium is then re-uptaked (a real word?) into the Sarcoplasmic reticulum. There is also Calcium that enters the cell from the extracellular space, but the major storage space for calcium is the SR. Hope that helps.

 

[FutureInternist]

Wow......a Fellow that still remembers basic physiology. And you even used the word "calmodulin"...... Awesome 😀

 

[EMCC]

What can I say?? Critical Care is all basic phsyiology--only with real life consequences... So, for all you med studs looking at critical care--SAVE YOUR BASIC PHYSIO TEXT!!!!!!!!

😀

 

[butaloh666]

There is very little "free floating calcium" in the cytoplasm at rest. When an action potential (electrical impulse), however, comes at the cell, the Sarcoplasmic Reticulum dumps a whole bunch of calcium into the cytoplasm to bind to Calmodulin et. al to cause contraction. When the impulse stops, the calcium is then re-uptaked (a real word?) into the Sarcoplasmic reticulum. There is also Calcium that enters the cell from the extracellular space, but the major storage space for calcium is the SR. Hope that helps.

This is a good explanation, but if I could just make one minor comment, I believe the influx of extra-cellular Ca during a contraction cycle is only a component of cardiac myocyte contraction and not skeletal myocytes.

 

[EMCC]

It is true that cardiac muscle "requires" extracellular Calcium, in addition to intracellular Calcium, for a contraction to take place.

Skeletal muscle (both smooth and voluntary) also uses a small amout of extracellular Calcium. The majority of the calcium does come from T tubules and Sarcoplasmic Reticulae. There have been a few studies that have demonstrated the role of extracellular Calcium in contraction of skeletal muscles.

What is not clear to me, and someone closer to basic science may be able to clear this up for me is: Does the role of extracellular calcium affect only Ca channels (presynaptic) or does it play a direct role in the force/strength of the contraction??

I know, I know, irrelevant basic science question. Sorry!

 

[dbhvt]

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