And there are many other examples of ptype Atpas that we'll study in the future lecture. For instance, we're going to also look at the sodium potassium Atpas, which is also an example of a ptype Atpas. Now, where exactly do we find and what membrane do we find these calcium ATPases? Well, remember, from basic biology, calcium is used by muscle cells. And so what that implies is the calcium Atpas must be found within muscle cells. And that's exactly right.