The mystery of calcium ions in myocytes

[eager cedar]

Dm me the answer or post it here but as spoilered messages! The discussion doesn't have to be spoilered, only the final answer

[heady valley]

@eager cedar very easy, ||I'll refer them to a primary physician||

[spare quartz]

because the cell is funny

[nova kelp]

so to simply put. when injecting calcium ion into normal muscle cell, will make this muscle cell contract. but doing the same on heart muscle cell will make this heart muscle cell not only contract but also secrete more calcium ion?

[eager cedar]

yes! more calcium ions will be found in the cytoplasm than just those injected

[nova kelp]

is that secreated ion or more ion inside the cell?

[eager cedar]

more ion inside the cell. in the cytoplasm!

[nova kelp]

would that increased calcium ion. trigger other heart cells to contract and secreat calcium ion?

[eager cedar]

Idk research that :D although I don't see how it helps you find the answer to this question specifically

[nova kelp]

he basically confirmed me

[tepid maple]

||would it be because striated cells couple dhp with the RyRs for calcium release, whereas cardiac muscle uses calcium to activate calcium release? So the cardiac myocyte has extra calcium since it released some of its own||

[jovial jetty]

Cardiac and striated myocytes probably behave differently and structurally differ

Cardiac muscles are justifiably distinguished

[bright prawn]

Feeling cardiac myocytes has to do with very regulated ion concentration level for the regulated and regular pulses from the very functional side

Whereas normie normal myocytes would pretty much controlled by voluntary controls from your brain, the cardiac ones has to do on their own, thus the additional regulation of calcium ion concentration when getting the influx from the injection

[nova kelp]

and which cause other heart cells to contract? and make heart beat?

[tepid maple]

I'm not sure about the details of intracellular communication between the cardiac myocytes, but the coordination of the whole cardiac muscle (the heart) should be controlled by the brain

[tepid maple]

I think the question's just talking about a single cardiac myocyte (I could be wrong tho!)

[glacial lion]

ah shit bio again

[mortal thicket]

But the heart contracts even when disconnected from the central nervous system, coordination between its cells is assured by its autonomous nervous system, right ?

[tepid maple]

yay bio!

[slender anchor]

|| Calcium induced calcium release from the SR, calcium binds to RYR on the SR, releasing more calcium into the cytoplasm ||

[slender anchor]

No, cardiac coordination is present without an ANS, you do have things like heart rate changes though

[tepid maple]

ooh i didnt know that! makes sense tho in the case of brain-dead patients.

[mortal thicket]

||I had a little idea, the Calcium Induced Calcium Release, by liberation of calcium from sarcoplasmic reticulum by calcium bounding to its receptors on the sarcoplasmic reticulum, but that applies to any striated cell, which isn't what the question is referring to apparently||

[tepid maple]

||i was a bit confused about that too, but it seems that CICR is primarily used in the cardiac muscle (not sure tho)||

[mortal thicket]

Yes, the heart can contract when isolated from the organism, its default is 120 beatings per minute, the autonomous nervous system (sympathetic/parasympathetic) control its rate, contraction force depending on the organism's needs and situation

[mortal thicket]

It is afaik, but that's no difference in this case 🤷‍♂️

[mortal thicket]

Ah yeah I just meant the heart's own nervous system, not the sympathetic/parasympathetic

[tepid maple]

whoa! i always just thought that the heart was controlled by the cns and ans 😅

[tepid maple]

i just figured it was used more in cardiac than striated, so thats why there was a difference. i dont actually know tho

[mortal thicket]

Actually the autonomous plays a vital role by controlling the heart rate, but yeah it's not necessary for simple contraction

[mortal thicket]

That may be it then

[tepid maple]

the nervous system always sounds so messy lol

[mortal thicket]

Yeah hahahahha

But it's fascinating aswell !

[slender anchor]

its dominated by vagal tone, but its generated by the SA node normally

[tepid maple]

i remember always stressing about my tests on brain function because all the regions seemed so interconnected lol

[tepid maple]

it definitely is!

[fluid jetty]

||I think the short answer would be the difference in EC coupling (excitation-contraction coupling) AFTER influx of calcium though L-type channles (or in this case from a injection), where in the cardiac myocytes it happens throughout a process called calcium-induced calcium release (CICR), and in the striated myocyes it happens as dihydropyridine receptor (DHPR)-ryanodine receptor (RYR) interactions.||

[neon plank]

so, milk ?

[willow fox]

||I guess it would be because presence of Ca ions triggers more ions to be released in a certain situation, like there might be more receptors that need to be triggered to cause contraction than injected or the receptors become less sensitive somehow to Ca ions, so the SR releases more to attain a higher amount of Ca ions in the cell...|| However, I am not certain. This is for the most part a guess based on what I think I have understood of what I have read

I need to read more

[mortal thicket]

I don't think bones are in a position to intervene in this short-term situation of cardiac myocytes contraction

[lone flax]

Is this an example of positive feedback?

[mortal thicket]

I think positive feedback is hormonal, this is not a hormonal response afaik

[lone flax]

So feedback only when hormones are present

[eager cedar]

Oops I forgot to send the answer here as well

ANSWER
|| The L calcium channel (a dihydropyridine receptor) in the T tubule is connected directly to the RYR receptor on the SR in the striated myocytes. Thus, its mandatory that L receptors get activated so that RYR also gets activated. (a in image)
In smooth and cardiac muscle however, the two aren't connected in their structure (they aren't a continuous structure) and the mechanism is just based on cytoplasmic levels of ionic calcium. (b in image)

Note: The L voltage gated calcium channels are also called dihydropyridine receptors because they have a binding place for dihydropyridine which blocks the activity of these channels. ||

[sullen moth]

||Cardiac myocytes utilize a specialized mechanism called calcium-induced calcium release (CICR). When calcium is introduced, it not only triggers contraction but also causes the release of additional calcium from internal stores, amplifying the contraction. This mechanism ensures synchronized and efficient heart muscle function.||

oh darn I just realised I was late