SERCA: Calcium Ion Pump - Online Tutor, Practice Problems & Exam Prep

The circa pump, or sarcoplasmic/endoplasmic reticulum calcium ATPase, is a P-type ATPase that functions as a uniporter, transporting calcium ions (Ca²⁺) into the sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER). This process lowers cytoplasmic calcium concentrations, crucial for cellular functions and muscle contractions. When calcium is released into the cytoplasm, it acts as an intracellular signal, inducing muscle contraction. Conversely, the circa pump facilitates muscle relaxation by decreasing cytoplasmic calcium levels, highlighting its role in calcium homeostasis and signaling pathways.

SERCA: Calcium Ion Pump

So now that we've covered the sodium potassium ATPase, in this video we're going to introduce yet another example of a P-type ATPase, which is the SERCA pump, which is really just a calcium ion pump as we'll see here very shortly. Now, SERCA is really just an abbreviation for sarcoplasmic or endoplasmic reticulum calcium ATPase. And SERCA really functions as a uniporter, which we'll see down below in our image. But recall from our previous lesson videos that uniporters will pump just one type of molecule across the membrane in one direction. And in this scenario, SERCA is pumping calcium ions or Ca2+ into either the sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER) depending on the cell type. And, of course, if it's constantly pumping calcium into the SR or ER, it's going to be keeping the cytoplasmic calcium concentrations really really low, and that's going to be very important for many different cell functions.

And so if we take a look at our image down below of the SERCA pump, notice that going across the top here, what we have is the cell's plasma membrane, which is separating the extracellular space here in blue from the inside of the cell or the cell cytoplasm. And notice that in the cytoplasm here, what we're showing you are 2 calcium ions. So we can go ahead and label these as calcium ions. And notice that below those calcium ions we have another membrane here, which is the sarcoplasmic reticulum membrane or endoplasmic reticulum membrane, depending again on the cell type. And notice that embedded in this SR or ER membrane, what we have is the SERCA pump that we're introducing here. And again, the SERCA pump is a classic example of a P-type ATPase, which means that it's going to get phosphorylated at some point to create a phosphorylated intermediate. And so you can see that down below it is utilizing ATP and hydrolyzing ATP into ADP. And in that process, the SERCA pump is actually getting phosphorylated itself. And so you can fill in the P here on the, representing the phosphate to show that SERCA is a P-type ATPase. And as it, gets phosphorylated, what it will do is actually take 2 calcium ions as we see here, and then it will pump these 2 calcium ions from the cytoplasm and pump them into the SR or ER. And so you should draw in this blue arrow here to remind you guys that calcium is getting pumped from the cytoplasm into the SR or ER in order to keep cytoplasmic calcium concentrations really really low.

And what's really important to note here is that when released into the cytoplasm, calcium actually has a very important role in pretty much all cells, and that's because it can act as an intracellular signal in virtually all cells. And later in our course when we're talking about bio-signaling we'll be able to talk about some specific pathways, bio signaling pathways that utilize calcium as an intracellular signal. But you might also recall in our previous lesson videos that we talked a little bit about muscle contractions. And so recall that muscle contractions will actually occur when a nerve impulse induces the release of calcium into the cytoplasm. And so you can see over here we have another pump embedded in the membrane that is utilized to release calcium into the cytoplasm. When calcium is in the cytoplasm, again it acts as an intracellular signal and can induce muscle contractions. And so you can see the calcium here can induce a muscle contraction. Increase of cytoplasmic calcium concentration. And so muscle contractions are associated with an increasing cytoplasmic concentration of calcium. Now of course we know that SERCA, the pump over here, is all about decreasing calcium concentrations in the cytoplasm. And so the SERCA pump will, again, pump calcium into the SR or ER, and so when it does that, it's actually going to allow for muscle relaxation to occur. And so it will occur when SERCA pumps calcium into the SR or ER, decreasing the cytoplasmic concentrations of calcium. And so here what we're saying is that increasing cytoplasmic calcium concentration leads to muscle contraction, whereas decreasing cytoplasmic calcium concentration leads to muscle relaxation. And again, that is what SERCA is going to be helping with. And so this here concludes our introduction to the SERCA calcium ion pump. As we move forward in our course, we'll be able to get some practice applying these concepts that we've learned. So I'll see you guys in our next video.

The calcium ATPase is an example of what type of transport model?

• A. Facilitated diffusion via antiport.
• B. Secondary active transport via symport.
• C. Primary active uniport.
• D. Simple diffusion.
• E. Primary active symport.

The calcium ATPase (SERCA) _____________________:

• A. Is a V-type ATPase that transports calcium inside vesicles.
• B. Is a P-type ATPase that maintains cytosolic [Ca²⁺] around 0.1 μM & sarcoplasmic reticulum [Ca²⁺] at 1.5 mM.
• C. Is a P-type ATPase and an example of passive facilitated diffusion.
• D. Is a P-type ATPase that transports calcium from the ER to the cytoplasm.
• E. None of the above are true.

Here’s what students ask on this topic:

What is the function of the SERCA pump in muscle cells?

The SERCA pump, or sarcoplasmic/endoplasmic reticulum calcium ATPase, plays a crucial role in muscle cells by regulating calcium ion (Ca²⁺) concentrations. It actively transports Ca²⁺ from the cytoplasm into the sarcoplasmic reticulum (SR), a specialized type of endoplasmic reticulum in muscle cells. This process lowers cytoplasmic Ca²⁺ levels, which is essential for muscle relaxation. When Ca²⁺ is released into the cytoplasm, it acts as a signal for muscle contraction. Therefore, the SERCA pump helps in muscle relaxation by reducing cytoplasmic Ca²⁺ concentrations, maintaining calcium homeostasis, and ensuring proper muscle function.

How does the SERCA pump utilize ATP in its function?

The SERCA pump is a P-type ATPase, meaning it uses ATP to transport calcium ions (Ca²⁺) across the membrane. During its operation, the pump hydrolyzes ATP to ADP and an inorganic phosphate (P_i). This hydrolysis provides the energy required for the pump to undergo conformational changes. Specifically, the pump gets phosphorylated, forming a phosphorylated intermediate. This phosphorylation drives the transport of two Ca²⁺ ions from the cytoplasm into the sarcoplasmic or endoplasmic reticulum (SR/ER). The dephosphorylation of the pump then resets it to its original state, ready for another cycle of Ca²⁺ transport.

Why is maintaining low cytoplasmic calcium concentration important in cells?

Maintaining low cytoplasmic calcium concentration is crucial for several reasons. First, Ca²⁺ acts as a secondary messenger in various cellular signaling pathways, including muscle contraction, neurotransmitter release, and enzyme activation. High cytoplasmic Ca²⁺ levels can lead to continuous activation of these pathways, causing cellular dysfunction. Second, prolonged high Ca²⁺ levels can activate enzymes that degrade cellular components, leading to cell damage or apoptosis. Therefore, mechanisms like the SERCA pump are essential to keep cytoplasmic Ca²⁺ concentrations low, ensuring proper cellular function and preventing damage.

What role does the SERCA pump play in muscle contraction and relaxation?

The SERCA pump is integral to the processes of muscle contraction and relaxation. During muscle contraction, a nerve impulse triggers the release of Ca²⁺ from the sarcoplasmic reticulum (SR) into the cytoplasm. The increased cytoplasmic Ca²⁺ concentration activates the contractile proteins, leading to muscle contraction. For muscle relaxation, the SERCA pump actively transports Ca²⁺ back into the SR, reducing the cytoplasmic Ca²⁺ levels. This decrease in Ca²⁺ concentration allows the muscle fibers to relax. Thus, the SERCA pump is essential for cycling between muscle contraction and relaxation by regulating Ca²⁺ levels.

How does the SERCA pump contribute to calcium homeostasis in cells?

The SERCA pump contributes to calcium homeostasis by actively transporting Ca²⁺ from the cytoplasm into the sarcoplasmic or endoplasmic reticulum (SR/ER). This action lowers cytoplasmic Ca²⁺ concentrations, which is crucial for various cellular functions. By maintaining low cytoplasmic Ca²⁺ levels, the SERCA pump ensures that Ca²⁺ can act as an effective intracellular signal when needed, without causing cellular damage or dysfunction. Additionally, it helps in muscle relaxation and prevents continuous activation of Ca²⁺-dependent pathways, thereby maintaining overall cellular health and function.