Ca2influx

Ca2influx refers to the movement of calcium ions (Ca2+) from the extracellular space into the cytosol across the plasma membrane, a key process in cellular signaling. Calcium acts as a universal second messenger, and influx serves to rapidly raise cytosolic Ca2+ in response to stimuli. Influx occurs through multiple channels and transport pathways, including voltage-gated Ca2+ channels, receptor-operated channels, store-operated channels, and ligand-gated receptors, with varying distributions across tissues.

Several major routes mediate Ca2influx. Voltage-gated Ca2+ channels (VGCCs) open in response to membrane depolarization and include L-, N-, P/Q-, R-, and T-type subtypes with tissue-specific roles. Receptor-operated and transient receptor potential (TRP) channels provide Ca2+ entry following receptor activation or physical stimuli. Store-operated calcium entry (SOCE) is activated when endoplasmic reticulum Ca2+ stores are depleted; STIM1 senses this depletion and gates Orai1 channels in the plasma membrane to permit Ca2+ influx. In neurons, NMDA receptors allow Ca2+ entry when activated by ligands and relieved of Mg2+ block by depolarization. Calcium influx through these pathways often cooperates with intracellular stores to shape signaling events.

Physiological roles of Ca2influx are diverse. It triggers neurotransmitter release, muscle contraction, hormone secretion, enzyme activity, and gene expression. At the molecular level, Ca2+ activates sensors such as calmodulin, which in turn regulate kinases, phosphatases, and transcription factors, coordinating complex signaling networks. Calcium influx is tightly regulated by buffering proteins, active pumps (PMCA, NCX), and sequestration in organelles (ER/SERCA pumps, mitochondria via MCU).

Dysregulation of Ca2+ influx is linked to pathology, including excitotoxicity, ischemia, and cardiac arrhythmias. Experimental measurement often uses fluorescent indicators (e.g., Fura-2, Fluo-4) and electrophysiological techniques to quantify influx dynamics and channel activity.