- Cardiac activity is dependent on the concentration of intracellular and extracellular ions.
- Many of the drugs used in clinical practice for cardiac ailments act by modulating the ionic concentration of cardiac cells.
Q1. What are the effects of the above ions on frog’s heart?
Sodium Chloride (NaCl)
- Facilitates depolarisation and hence increases the heart rate. But it competes with calcium ions and therefore decreases the force of contraction.
Potassium Chloride
- Decrease the resting membrane potential, therefore the fibers become inexcitable. Heart stops in diastole.
Calcium chloride
- Increase the force of contraction and decreases the relaxation time, therefore the heart stops in systole (tonic contraction) – Calcium Rigor
Q2. What is calcium rigor?
- Calcium chloride increase the force of contraction and decreases the relaxation time, therefore the heart stops in systole (tonic contraction) – Calcium Rigor.