Temporal and spatial dynamics underlying capacitative calcium entry in human colonic smooth muscle

Area of Science:

• Physiology
• Cell Biology
• Gastroenterology

Background:

• Smooth muscle contraction relies on intracellular calcium (Ca2+).
• Depletion of intracellular Ca2+ stores triggers capacitative Ca2+ entry (CCE) to sustain elevated cytoplasmic Ca2+ (Ca2+(i)).

Purpose of the Study:

• To characterize CCE and Ca2+(i) dynamics in human colonic smooth muscle contraction.
• Investigate the role of CCE in colonic smooth muscle function.

Main Methods:

• Tension recordings in tissue strips.
• Fluorescent Ca2+-indicator dyes for Ca2+(i) measurements.
• Patch-clamp electrophysiology on isolated smooth muscle cells (SMCs).
• Sarcoplasmic reticulum Ca2+-ATPase (SERCA) inhibitors (thapsigargin, cyclopiazonic acid).
• High-speed Ca2+-imaging.

Main Results:

• Acetylcholine (ACh) induced contraction, Ca2+(i) elevation, and cation currents in colonic SMCs.
• SERCA inhibition in Ca2+-free solution followed by extracellular Ca2+ addition induced tension, suggesting CCE.
• CCE-evoked Ca2+(i) rise was linked to inward currents inhibited by SKF-96365 and lanthanum.
• Distinct "hotspot" regions of Ca2+ influx and plateau were observed in 70% of cells during CCE.

Conclusions:

• Store-operated Ca2+ entry (CCE) occurs in human colonic smooth muscle.
• CCE is mediated by cation currents and contributes to Ca2+(i) elevations.
• Localized Ca2+ influx via "hotspots" is a novel feature of CCE in human colonic smooth muscle.