Question

Under “baseline” conditions, cytosolic concentrations of 2nd messengers like Ca2+ are very low. Why do you think that is? What advantage does it provide?

Answer 1

Calcium levels are maintained at very low concentrations intracellularly via its removal to the extracellular environment and sequestration in the endoplasmic reticulum. As such, it is a powerful second messenger important in proliferation, differentiation, mitosis, and motility. Binding of Ca2+ to calmodulin activates this protein, which then initiates its effects by binding to still other downstream targets, such as protein kinases. Ordinarily the concentration of Ca2+ ions in the cytosol is extremely low, typically 50–100 nanomolar (10–9 M). The low concentration of calcium in the cytosol allows calcium ions to function as a second messenger in calcium signaling. Here, a signal such as a hormone or an action potential opens calcium channel so that calcium floods into the cytosol.

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