Experimental stimulation of the sympathetic nerve branches that innervate the heart caused an increase in the force of heart contractions because the membrane of typical cardiomyocytes permitted an increase in:

Answer options

1. Calcium and potassium ion exit
2. Potassium ion entry
3. Calcium ion exit
4. Calcium ion entry
5. Potassium ion exit

Explanation

Excitation-contraction (EC) coupling in cardiac myocytes is mediated by the entry of calcium ions (Ca2+) from the bathing medium into the cell cytoplasm. action potential subsequently triggers muscle contraction by increasing the concentration of calcium.