Which statements accurately describes the regulation of cont

Which statement(s) accurately describe(s) the regulation of contraction strength of myocardial cells?

a) The higher the intracellular concentration of Ca2+, the stronger the force of contraction will be.

b) Catecholamines make voltage-gated Ca2+ channels more likely to open, thus allowing higher concentrations of Ca2+ inside the cell.

c) The higher the intracellular concentration of Ca2+, the more crossbridges will be active.

d) Only A and B are true

e) A, B and C

Solution

All the statements above i.e. a), b) and c) are correct. (Option e)

During an action potential, the increasing contractility of the myocardial cells is generally done by increasing the calcium ion influx or maintaining the higher calcium levels in the cytosol of cardiac myocytes. Phosphorylating L-type calcium channels will increase their permeability to calcium, allowing more calcium into the myocyte cells, increasing contractility. Therefore \"The higher the intracellular concentration of Ca2+, the stronger the force of contraction will be.\"

Catecholamine is a monoamine derived from the amino acid tyrosine. It activates beta-adrenergic receptors in the heart to produce a G-protein mediated increase in cAMP and enhanced activity of a cAMP-dependent protein kinase .This leads to the phosphorylation of calcium membrane channels and enhances calcium entry into the myocardial cell \"thus allowing higher concentrations of Ca2+ inside the cell.\"

At low intracellular Ca²⁺ concentration, tropomyosin blocks the active sites on actin therefore myosin heads cannot attach to actin and muscle fiber relaxes. At higher intracellular Ca²⁺ concentrations, Calcium ion binds to troponin. Troponin changes shape and moves tropomyosin away from active sites and events of the cross bridge cycle occur. So \"higher the intracellular concentration of Ca^2+, the more crossbridges will be acive\".