TRP channel Ca2+ sparklets: fundamental signals underlying endothelium-dependent hyperpolarization

Abstract

Important functions of the vascular endothelium, including permeability, production of antithrombotic factors, and control of vascular tone, are regulated by changes in intracellular Ca2+. The molecular identities and regulation of Ca2+ influx channels in the endothelium are incompletely understood, in part because of experimental difficulties associated with application of patch-clamp electrophysiology to native endothelial cells. However, advances in confocal and total internal reflection fluorescence microscopy and the development of fast, high-affinity Ca2+-binding fluorophores have recently allowed for direct visualization and characterization of single-channel transient receptor potential (TRP) channel Ca2+ influx events in endothelial cells. These events, called “TRP channel Ca2+ sparklets,” have been optically recorded from primary endothelial cells and the intact endothelium, and the biophysical properties and fundamental significance of these Ca2+ signals in vasomotor regulation have been characterized. This review will first briefly discuss the role of endothelial cell TRP channel Ca2+ influx in endothelium-dependent vasodilation, describe improved methods for recording unitary TRP channel activity using optical methods, and highlight discoveries regarding the regulation and physiological significance of TRPV4 Ca2+ sparklets in the vascular endothelium enabled by this new technology. Perspectives on the potential use of these techniques to evaluate changes in TRP channel Ca2+ influx activity associated with endothelial dysfunction are offered.