Final answer:
Calcium ions (Ca2+) enter cells through various gated channels and bind to proteins like calmodulin and troponin, triggering physiological responses such as muscle contractions. Highest Ca2+ concentrations are present in the extracellular fluid. Ca2+ plays a versatile role in cellular processes.
Step-by-step explanation:
Among the statements provided about calcium ions (Ca2+), there are certain true aspects relevant to Ca2+ physiological roles and mechanisms in the cell:
Ca2+ enters cells through Ca2+ channels that can be voltage-, ligand-, or mechanically-gated.
Ca2+ binds to the protein calmodulin.
Most intracellular Ca2+ is stored within cytoplasmic compartments such as the sarcoplasmic or endoplasmic reticulum, not the nucleus.
Ca2+ binding to the regulatory protein troponin initiates muscle contraction, not relaxation.
Ca2+ concentration is higher in the extracellular fluid (ECF) compared with the intracellular fluid (ICF).
The exchange of Ca2+ through cellular mechanisms is crucial for various cellular processes, including muscle contractions and neurotransmitter release at synapses. The role of Ca2+ is multifaceted, depending on the cell type and context within the physiological processes.