Histaminergic H1-receptors in smooth muscle and endothelium of bovine thoracic aorta

Role of tissue transglutaminase-2 (TG2)-mediated aminylation in biological processes

Post-translational modification (PTM) is an important mechanism in modulating a protein's structure and can lead to substantial diversity in biological function. Compared to other forms of PTMs such as phosphorylation, acetylation and glycosylation, the physiological significance of aminylation is limited. Aminylation refers to the covalent incorporation of biogenic/polyamines into target protein by calcium-dependent transglutaminases (TGs). The development of novel and more sensitive techniques has led to more proteins identified as tissue transglutaminase (TG2) substrates and potential targets for aminylation. Many of these substrate proteins play a role in cell signaling, cytoskeleton organization, muscle contraction, and inflammation. TG2 is well studied and widely expressed in a variety of tissues and will be the primary focus of this review on recent advance in transglutaminase-mediated aminylation.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

The role of histamine in dural vessel dilation

The pain of migraine is often throbbing suggesting an important role for the cranial blood vessels and their innervation by the trigeminal nerve. It is proposed that clinically effective anti-migraine compounds, such as 5-HT(1B/1D) agonists, have actions that include inhibiting calcitonin gene-related peptide (CGRP) release from trigeminal nerves. Human studies suggest that histamine can induce migraine possibly by activating nitric oxide (NO) synthase to promote endogenous NO production. The present studies investigated the effect of histamine and its antagonists on the cranial blood vessels using intravital microscopy to assess directly the diameter of dural arteries in sodium pentobarbitone anaesthetised rats. Electrical stimulation of a closed cranial window produces, by local depolarisation of nerves, dural vessel dilation that is monitored continuously on-line using video-microscopy and a video dimension analyser. Histamine infusion caused immediate and reproducible dilation of meningeal blood vessels (103.5+/-6%; n=40) that could be blocked by H(1)- (mepyramine) and H(2) (famotidine)-receptor antagonists (P<0.05), as well as a nitric oxide synthase inhibitor (N(G)-nitro-L-arginine methylester; P<0.05). Neurogenic dural vasodilation was not inhibited by H(2)-receptor antagonists, but was significantly inhibited by a H(1)-receptor antagonist at the high dose of 10 mg/kg. The present studies demonstrate that histamine is likely to activate NO synthase to promote NO production. There is also evidence that H(1)-receptors may be present on trigeminal neurones as the H(1)-receptor antagonist inhibited neurogenic vasodilation, albeit at a large dose.