Ca2sensorer

Ca2+-sensors are molecules or devices that detect calcium ions (Ca2+) and convert changes in Ca2+ concentration into a measurable signal. In biology, Ca2+ serves as a universal second messenger, and cells rely on rapid, localized Ca2+ fluctuations to regulate processes such as muscle contraction, neurotransmitter release, gene expression, and enzyme activity. Calcium sensors can be classified as intracellular sensors, extracellular sensors, and synthetic indicators.

Intracellularly, many Ca2+-binding proteins act as sensors. Proteins with EF-hand motifs, such as calmodulin and troponin C, bind Ca2+ and undergo conformational changes that modulate their target proteins, translating Ca2+ signals into altered activity within the cell.

For imaging and measurement, two broad classes are used: genetically encoded calcium indicators (GECIs) and chemical indicators. GECIs, such as the GCaMP family, fuse a Ca2+-binding domain with a fluorescent protein and brighten or shift fluorescence when Ca2+ binds, enabling live-cell or in vivo imaging. Chemical indicators like Fura-2, Fluo-4, and Indo-1 are small molecules that increase fluorescence upon Ca2+ binding and can be used with ratiometric measurements to quantify Ca2+ levels.

Extracellular calcium sensing is performed by receptors such as the calcium-sensing receptor (CaSR), a G-protein coupled receptor that detects extracellular Ca2+ concentrations and modulates hormone secretion and renal Ca2+ handling.

Applications include basic research in neuroscience and physiology, drug screening, and the development of diagnostic tools. Important considerations when using Ca2+-sensors include the sensor’s affinity (Kd), dynamic range, and potential buffering effects on cellular Ca2+ signaling.