Calcium Ions as Intracellular Messengers

Abstract

Calcium acts as both an extracellular (first) and an intracellular (second) messenger to regulate a diverse array of cellular functions, from cell division and differentiation to cell death. Accordingly, Ca²⁺ concentration in the plasma, as well as in the intercellular and intracellular environment, is under tight neuronal and hormonal control. The availability of Ca²⁺ for controlling Ca²⁺ concentration in the plasma and extracellular environment is secured from both diet and the bone matrix, thereby preventing any risk of Ca²⁺ deprivation. Changes in the extracellular free Ca²⁺ concentration ([Ca²⁺]_e) signal the activation of Ca²⁺-sensing receptors, which act to restore basal [Ca²⁺]_e. Although these receptors are found in several tissues, those expressed in parathyroid cells are intimately involved in the control of [Ca²⁺]_e. This chapter focuses on the role of Ca²⁺ as an intracellular messenger and the pathways that regulate its intracellular concentration. All selected references are review articles that can direct the readers to more specific aspects of Ca²⁺ signaling. Also, several chapters in this textbook are critical for understanding some of the aspects of Ca²⁺ signaling. This includes, but is not limited to, chapters on Ca²⁺ and Ca²⁺-binding proteinmediated pathways, G protein-coupled receptors, phospholipases, adenylyl cyclases, protein kinase, ion channels, and apoptosis.