Transcellular openings through frog microvascular endothelium

Area of Science:

• Cell biology
• Microcirculation research
• Endothelial cell physiology

Background:

• Microvascular endothelium plays a crucial role in regulating blood flow and permeability.
• Previously, gaps in endothelium were thought to occur only between endothelial cells.
• The possibility of gaps forming within endothelial cells (transcellular) and fixation artifacts needed investigation.

Purpose of the Study:

• To determine if gaps in microvessels can occur transcellularly (through endothelial cells).
• To investigate if aldehyde fixation methods might create artifacts resembling transcellular gaps.
• To provide evidence for or against the existence of true transcellular gaps in microvasculature.

Main Methods:

• Serial ultrathin sectioning and reconstruction of microvascular endothelium.
• Induction of gaps using the ionophore A23187 in frog mesenteric microvessels.
• Primary fixation using osmium tetroxide, an alternative to aldehyde fixatives.

Main Results:

• Fourteen gaps induced by A23187 were reconstructed.
• All fourteen reconstructed gaps were found to be transcellular, passing through endothelial cells.
• The use of osmium tetroxide, distinct from aldehyde fixatives, supports the reality of these gaps.

Conclusions:

• Transcellular gaps in microvasculature are likely real phenomena, not artifacts of aldehyde fixation.
• Endothelial cells possess mechanisms allowing for the formation of transcellular pathways.
• This finding has implications for understanding microvascular permeability and transport mechanisms.