Gastrointestinal smooth muscle calcium handling

Gastrointestinal (GI) smooth muscle calcium handling refers to the integrated physiological processes that regulate intracellular calcium concentrations ([Ca2+]i) to drive the contraction and relaxation of the gut wall. Contraction is primarily initiated when excitatory stimuli trigger calcium influx through voltage-gated L-type calcium channels (Cav1.2) or release from the sarcoplasmic reticulum via inositol trisphosphate (IP3) and ryanodine receptors. This rise in [Ca2+]i activates myosin light chain kinase (MLCK), which phosphorylates the regulatory light chain of myosin to initiate cross-bridge cycling and force generation. Relaxation is achieved by lowering [Ca2+]i through sequestration into the sarcoplasmic reticulum by SERCA pumps and extrusion from the cell via the plasma membrane calcium ATPase (PMCA) and sodium-calcium exchangers (NCX). These mechanisms are also influenced by interstitial cells of Cajal (ICC), which act as pacemakers and modulate smooth muscle excitability through calcium-dependent conductances. Dysregulation of these calcium handling mechanisms is central to the pathophysiology of various GI motility disorders, including irritable bowel syndrome (IBS), achalasia, and gastroparesis. Therapeutic strategies often involve the use of calcium channel blockers (CCBs) to reduce smooth muscle tone and alleviate spasms. While systemic CCBs like nifedipine are effective, they are often limited by cardiovascular side effects, leading to the development of gut-selective agents like pinaverium bromide to improve safety and efficacy.

Other names

Gut smooth muscle Ca2+ handling mechanismsGastrointestinal smooth muscle calcium signalingGI smooth muscle excitation-contraction couplingGut calcium handling

Regulation of smooth muscle contractility by modulating intracellular calcium levels through the inhibition of voltage-gated calcium channels, the modulation of sarcoplasmic reticulum calcium release, or the enhancement of calcium extrusion pathways to regulate smooth muscle tone and motility.