Calcium and potassium ions have important effects on all cells but do not direct
ID: 224932 • Letter: C
Question
Calcium and potassium ions have important effects on all cells but do not directly bind to ligand-gated receptors. An increase in the intracellular Ca^2+ concentration is responsible for muscle contraction in all types of muscle. In cardiac muscle cells, the influx of Ca^2+ is also responsible for the ____ phase of each cardiac action potential. When exogenous Ca^2+ is added to the fluid surrounding the heart, this will _______ the normal concentration gradient for calcium. What do you predict will happen to heart rate and contractility with the addition of Ca^2+?Explanation / Answer
Please find the answers below:
Blank 1: Repolarization
Blank 2: Increase
Reasons: The cardiac potential represents a closely coupled activation of the cardiac muscles in response to inwards and outwards movement of cations and anions. The calcium ions play a most curcial role in this phenomenon. Here, as the intracellular calcium concentration increases, the excitability of the cardiac muscles also increases. The increase in inward flow of calcium ion further opens up the store-operated calcium channels in the myocyte from the sarcoplasmic reticulum and thus increase the force of contraction by gradual repolarization of the muscle. Further, extracellular increase in total calcium ions further increase the intracellular calcium content due to un-restricted inflow of calcium until saturation and hence further enhance the cardiac contractibility due to sudden repolarization.
Thus, cardiac contractibility is closely coupled to calcium ion concentration.