[Capacitative Ca²⁺ entry is involved in ACh-induced distal colon smooth muscle contraction in rats]

Area of Science:

• Physiology
• Pharmacology
• Cell Biology

Context:

• Smooth muscle cell contraction is regulated by cytosolic calcium (Ca2+) levels.
• Calcium influx through plasma membrane channels is crucial for agonist-induced smooth muscle responses.
• While voltage-operated calcium channels (VOCC) were traditionally implicated, other channels like store-operated calcium channels (SOCC) are increasingly recognized.

Purpose:

• To investigate the role of capacitative calcium entry (CCE) mediated by SOCC in acetylcholine (ACh)-induced contractions of rat distal colon smooth muscle.
• To determine if SOCC contributes to contractile responses beyond the known role of VOCC.

Summary:

• ACh and high extracellular K+ induced contractions in rat distal colon smooth muscle, dependent on extracellular Ca2+.
• Verapamil, an L-type VOCC blocker, partially inhibited these contractions, suggesting involvement of other Ca2+ entry pathways.
• Lanthanum (La3+), an SOCC inhibitor, dose-dependently suppressed Ca2+ readdition-induced contractions, confirming SOCC's role in CCE and smooth muscle contraction.

Impact:

• Demonstrates that both VOCC and SOCC mediate Ca2+ influx in rat distal colon smooth muscle contraction.
• Highlights the significant contribution of SOCC-mediated CCE to agonist-induced contractile responses in this tissue.
• Provides a more comprehensive understanding of the molecular mechanisms underlying smooth muscle contractility in the gastrointestinal tract.