Pressure‐dependent regulation of Ca ²⁺ signalling in the vascular endothelium

Abstract

Key points

• Increased pressure suppresses endothelial control of vascular tone but it remains uncertain ( 1) how pressure is sensed by the endothelium and (2) how the vascular response is inhibited.

• This study used a novel imaging method to study large numbers of endothelial cells in arteries that were in a physiological configuration and held at normal blood pressures.

• Increased pressure suppressed endothelial IP ₃‐mediated Ca ²⁺ signals.

• Pressure modulated endothelial cell shape.

• The changes in cell shape may alter endothelial Ca ²⁺ signals by modulating the diffusive environment for Ca ²⁺ near IP ₃ receptors.

• Endothelial pressure‐dependent mechanosensing may occur without a requirement for a conventional molecular mechanoreceptor.

Abstract

The endothelium is an interconnected network upon which haemodynamic mechanical forces act to control vascular tone and remodelling in disease. Ca ²⁺ signalling is central to the endothelium's mechanotransduction and networked activity. However, challenges in imaging Ca ²⁺ in large numbers of endothelial cells under conditions that preserve the intact physical configuration of pressurized arteries have limited progress in understanding how pressure‐dependent mechanical forces alter networked Ca ²⁺ signalling. We developed a miniature wide‐field, gradient‐index (GRIN) optical probe designed to fit inside an intact pressurized artery that permitted Ca ²⁺ signals to be imaged with subcellular resolution in a large number (∼200) of naturally connected endothelial cells at various pressures. Chemical (acetylcholine) activation triggered spatiotemporally complex, propagating inositol trisphosphate (IP ₃)‐mediated Ca ²⁺ waves that originated in clusters of cells and progressed from there across the endothelium. Mechanical stimulation of the artery, by increased intraluminal pressure, flattened the endothelial cells and suppressed IP ₃‐mediated Ca ²⁺ signals in all activated cells. By computationally modelling Ca ²⁺ release, endothelial shape changes were shown to alter the geometry of the Ca ²⁺ diffusive environment near IP ₃ receptor microdomains to limit IP ₃‐mediated Ca ²⁺ signals as pressure increased. Changes in cell shape produce a geometric microdomain regulation of IP ₃‐mediated Ca ²⁺ signalling to explain macroscopic pressure‐dependent, endothelial mechanosensing without the need for a conventional mechanoreceptor. The suppression of IP ₃‐mediated Ca ²⁺ signalling may explain the decrease in endothelial activity as pressure increases. GRIN imaging provides a convenient method that gives access to hundreds of endothelial cells in intact arteries in physiological configuration.

Key points

• Increased pressure suppresses endothelial control of vascular tone but it remains uncertain ( 1) how pressure is sensed by the endothelium and (2) how the vascular response is inhibited.

• This study used a novel imaging method to study large numbers of endothelial cells in arteries that were in a physiological configuration and held at normal blood pressures.

• Increased pressure suppressed endothelial IP ₃‐mediated Ca ²⁺ signals.

• Pressure modulated endothelial cell shape.

• The changes in cell shape may alter endothelial Ca ²⁺ signals by modulating the diffusive environment for Ca ²⁺ near IP ₃ receptors.

• Endothelial pressure‐dependent mechanosensing may occur without a requirement for a conventional molecular mechanoreceptor.