Signaling via Ion Channels

Ion channels are membrane proteins that allow ions to pass through.  In terms of ion selectivity, they are classified as calcium channels, sodium channels, potassium channels, etc.  In terms of gating (how channels are opened), they may be classified as voltage-gated channels, ligand-gated channels, etc.

Figure 6-C-1.  Two types of Ca²⁺ channels. (1) The voltage-activated Ca²⁺ channels located on the plasma membrane. (2) The IP₃-sensitive Ca²⁺ channels located on the membrane of endoplasmic reticulum.

The major role of sodium and potassium ions is to regulate membrane potential.  However, the calcium ion also plays important roles in other cellular functions, since many enzymes are calcium-dependent.  The above figure shows two pathways that Ca²⁺ may enter the cytosol.

1. Through voltage-activated Ca²⁺ channels whose opening probability depends on the membrane potential.
2. Through IP₃-sensitive Ca²⁺ channels whose opening probability is regulated by IP₃ (inositol trisphosphate). 

The opening of Ca²⁺ stores in the endoplasmic reticulum may result in  calcium waves.

Calmodulin is an important molecule that can bind to Ca²⁺ to modulate its activity.

Review Articles:

Regulation of smooth muscle calcium sensitivity: KCl as a calcium-sensitizing stimulus - Am. J. Physiol., 2005.

Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP)-mediated Calcium Signaling - J. Biol. Chem., 2005.

Calcium, ATP, and ROS: a mitochondrial love-hate triangle - Am. J. Physiol., 2004.

Control of Cardiac Growth and Function by Calcineurin Signaling - J. Biol. Chem., 2003.

Structure–function of the multifunctional Ca²⁺/calmodulin-dependent protein kinase II - Biochem. J., 2002.

Structure–function of the multifunctional Ca²⁺/calmodulin-dependent protein kinase II - Biochem. J., 2002.

Calcium signaling: A tale for all seasons - PNAS, 2002.

Extracellular Calcium Sensing and Extracellular Calcium Signaling - Physiological Review, 2001.

Ca2+-dependent cell signaling through calmodulin-activated protein phosphatase and protein kinases - J. Biol. Chem., 2001.

Defining Ca²⁺/Calmodulin-dependent Protein Kinase Cascades in Transcriptional Regulation - J. Biol. Chem., 2001.

Cellular Signaling through Multifunctional Ca²⁺/Calmodulin-dependent Protein Kinase II - J. Biol. Chem., 2001.

Calcium, Calcineurin, and the Control of Transcription - J. Biol. Chem., 2001.

Dedicated Myosin Light Chain Kinases with Diverse Cellular Functions - J. Biol. Chem., 2001.

Transmembrane Redox Sensor of Ryanodine Receptor Complex - J. Biol. Chem., 2000.