Spatial microenvironment defines Ca2+ entry and Ca2+ release in salivary gland cells

Area of Science:

• Cellular Physiology
• Gastrointestinal Physiology

Background:

• Muscarinic receptor activation influences calcium (Ca2+) mobilization in salivary glands.
• Parotid acinar and duct cells exhibit distinct cellular functions and responses.

Purpose of the Study:

• To investigate the differences in Ca2+ mobilization induced by muscarinic receptor activation between parotid acinar and duct cells.
• To elucidate the underlying molecular mechanisms, particularly the role of inositol trisphosphate receptors (IP3Rs) and their localization.

Main Methods:

• Reverse transcription polymerase chain reaction (RT-PCR) to identify receptor expression.
• Immunocytochemistry to determine the cellular localization of receptors and IP3R2.
• Stimulation with muscarinic agonist (oxotremorine) and purinergic agonist (ATP) to assess Ca2+ mobilization.

Main Results:

• Oxotremorine induced both intracellular Ca2+ release and extracellular Ca2+ entry (via store-operated Ca2+ entry (SOC) and non-SOC channels) in acinar cells.
• In duct cells, oxotremorine activated only non-SOC channel-mediated Ca2+ entry.
• IP3R2 colocalized with M3 receptors in acinar cells but not in duct cells, where IP3R2 localized opposite to M3 receptors.
• Purinergic P2Y2 receptors colocalized with IP3R2 in the apical area of duct cells.

Conclusions:

• The spatial proximity of inositol trisphosphate receptors (IP3Rs) to G-protein-coupled receptors (like M3) is crucial for activating intracellular Ca2+ stores.
• Cellular microenvironment and receptor localization significantly influence intracellular Ca2+ release and entry pathways in salivary gland cells.