Thrombin Induces Inositol Trisphosphate-Mediated Spatially Extensive Responses in Lung Microvessels

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• Plasma membrane receptor activation triggers localized second messenger signaling.
• The intercellular diffusion patterns of these second messengers remain poorly understood.
• Understanding these pathways is key to comprehending inflammatory response amplification.

Purpose of the Study:

• To investigate the intercellular diffusion of second messengers following receptor activation.
• To determine the specific second messenger responsible for amplifying inflammatory responses in lung microvessels.
• To explore the role of connexin43 in mediating this intercellular signaling.

Main Methods:

• Thrombin was applied to restricted microvessel regions in blood-perfused mouse lungs.
• Endothelial F-actin and cytosolic Ca2+ oscillations were measured using confocal fluorescence microscopy.
• Inositol trisphosphate signaling was inhibited using Xestospongin C (XeC).
• Experiments were conducted in wild-type and connexin43-deficient mice.

Main Results:

• Thrombin induced F-actin increases in both treated and adjacent untreated microvessels.
• Xestospongin C (XeC) blocked these increases, indicating inositol trisphosphate (IP3) diffusion.
• IP3, not Ca2+, diffused between endothelial cells to propagate the signal.
• The response was absent in mice lacking endothelial connexin43, highlighting its role.

Conclusions:

• Receptor-mediated agonists amplify inflammatory responses via intercellular IP3 diffusion, distinct from cell-wide Ca2+ signals.
• Connexin43 gap junctions are essential for this spatially extensive signaling.
• Compartmentalized signaling and interendothelial communication dictate the inflammatory response.