Questions: Question 3 1 pts In cardiac muscle, Ca 2+ re-uptake into the sarcoplasmic reticulum requires the and also exits the cell through the Ca 2+ ATPase pump, sodium-calcium exchanger Actin, myosin Troponin, ryanodine receptor

The answer is the first one: Ca²⁺ ATPase pump, sodium-calcium exchanger.

Explanation for each option:

1. Ca²⁺ ATPase pump, sodium-calcium exchanger: This is the correct answer. In cardiac muscle, Ca²⁺ re-uptake into the sarcoplasmic reticulum is facilitated by the Ca²⁺ ATPase pump (also known as SERCA - Sarcoplasmic Reticulum Ca²⁺ ATPase). Additionally, Ca²⁺ exits the cell through the sodium-calcium exchanger, which helps maintain calcium homeostasis by exchanging intracellular Ca²⁺ for extracellular Na⁺.

2. Actin, myosin: This option is incorrect. Actin and myosin are proteins involved in muscle contraction, not in the re-uptake or exit of Ca²⁺ in cardiac muscle cells.

3. Troponin, ryanodine receptor: This option is incorrect. Troponin is a regulatory protein that binds calcium to facilitate muscle contraction, and the ryanodine receptor is involved in the release of Ca²⁺ from the sarcoplasmic reticulum, not in its re-uptake or exit from the cell.

In summary, the correct mechanisms for Ca²⁺ re-uptake and exit in cardiac muscle involve the Ca²⁺ ATPase pump and the sodium-calcium exchanger, respectively.