Definition: Given a passage and a query based on the passage, generate an unambiguous, concise and simple answer to the query from information in the passage. Note that the answer may not be present in exact form.
Input: Calcium is a chemical element. Its symbol on the periodic table is Ca. Its atomic number is 20. It has 20 protons and 20 electrons. The most common isotopes are Ca-40 and Ca-44. Its mass number is about 40.08. Calcium is very important in the human body, for making bones and for other purposes. As you state in the question, glucose enters the beta-cell and is metabolized creating an INCREASE in the ATP content of the cell. This increased ATP binds to ATP-sensitive potassium channels and CLOSES them. Inactivation and closure is an intrinsic property of that type of calcium channel, and the channels do not REACTIVATE until the cell returns to being polarized once again. This inactivation is what limits the amount of calcium flux INTO the cell, which as mentioned in the other answer can be toxic to the cell. Calcium is not found as a metal in the ground; it is too reactive. Calcium carbonate, also known as calcite, is the most common calcium mineral. Calcium in cells. It is important to know how cells work. Many cells have calcium channels on their surface. These are openings where calcium ions can enter the cell. The cell is told to act and it opens the channels. Once in the cell calcium ions activates many proteins to do specific things. When the cell reaches a threshold potential (that is, when it becomes depolarized to a certain point), it will cause opening of a type of voltage sensitive calcium channels. At this point, calcium channels open and allow calcium to flow down its concentration gradient and INTO the beta-cells. This calcium entry is required for the release of insulin vesicles through a mechanism that is outside the scope of this question, but unrelated to the calcium channels opening and closing. Remember, these channels are typically OPEN and allow potassium to normally flow OUT of the cell (because that would be potassium flowing DOWN its concentration gradient... potassium concentration is higher inside the cell than outside the cell). Note: This is the opposite for calcium, which would flow INTO the cell and down its concentration gradient (calcium outside the cell is higher than calcium inside the cell). At the same time the ATP-sensitive channels are acting, there are Na/K ATPase pumps at work to move sodium OUT of the cell and potassium INTO to the cell (against the concentration gradients of both those ions). How does excitation-contraction coupling in a cardiac muscle cell differ from that in a skeletal and smooth muscle fiber. Cardiac--depolarization due to influx of calcium ions through voltage gated channels (L type calcium channels which are modified versions of the DHP receptors in skeletal muscle). Cardiac--instead of being open directly by voltage as in skeletal muscle, cardiac are opened by binding of trigger calcium in cytosol. Mechanism by which individual muscle cells of the heart function as if they were a single unit, all undergoing synchronous electrical and mechanical activity. Cardiac muscles are joined by gap junctions that permit the conduction of action potential from cell to cell. This means that potassium can't leave the cell anymore, which depolarises the membrane and causes voltage-gated calcium channels to open and release calcium into the cell to trigger insulin release. I don't understand why this happens, because both potassium and calcium being positively charged. When it is in a chunk, it starts reacting slowly because calcium hydroxide makes a coating that does not dissolve on the calcium. If a little acid is added to calcium hydroxide, it dissolves it, making the calcium react very fast. It burns when powdered to make a reddish flame. This makes calcium oxide. Query: how does calcium enter the cell
Output:
Many cells have calcium channels on their surface. These are openings where calcium ions can enter the cell. The cell is told to act and it opens the channels.