AB5652P Sigma-AldrichAnti-Histamine Receptor 1 Antibody, CT

Some receptors and signaling molecules, such as Rho-kinase (ROCK), localize in caveolae. We asked whether the function of histamine receptors (H(1)) and 5-hydroxytryptamine (serotonin) receptors (5-HT(2A)) in bovine tracheal smooth muscle are modified after caveolae disruption and if so, whether the altered ROCK activity plays a role in this modification. Methyl-beta-cyclodextrin (MbetaCD), used to deplete membrane cholesterol, was shown to disrupt caveolae and diminish sustained contractions to histamine (approximately 80%), 5-HT (100%), alpha-methyl-5-HT (100%), and KCl (approximately 30%). Cholesterol-loaded MbetaCD (CL-MbetaCD) restored the responses to KCl and partially restored the responses to agonists. ROCK inhibition by Y-27632 diminished contractions to histamine (approximately 85%) and 5-HT (approximately 59%). 5-HT or histamine stimulation augmented ROCK activity. These increases were reduced by MbetaCD and partially reestablished by CL-MbetaCD. The increase in intracellular Ca(2+) that was induced by both agonists was reduced by MbetaCD. The presence of caveolin-1 (Cav-1), H1, 5-HT(2A), and ROCK1 was corroborated by immunoblotting of membrane fractions from sucrose gradients and by confocal microscopy. H(1) receptors coimmunoprecipitated with Cav-1 in caveolar and noncaveolar membrane fractions, whereas 5-HT(2A) receptors appeared to be restricted to noncaveolar membrane fractions. We conclude that caveolar and cholesterol integrity are indispensable for the proper functionality of the H(1) and 5-HT(2A) receptors through their Rho/ROCK signaling.

The aim of the present study was to investigate the effect of histamine, a product of e.g. mast cells, on short-circuit current (I(sc)) across rat distal colon. Histamine concentration-dependently stimulated an increase in I(sc), which often was preceded by a transient negative current. Neither a release of neurotransmitters nor a release of prostaglandins contributed to the histamine response. The histamine-induced increase in I(sc) was blocked by the histamine H(1) antagonist, pyrilamine, but was resistant against the histamine H(2) antagonist, cimetidine. Conversely, the histamine H(1) agonist, TMPH (2-(3-trifluoromethylphenyl)histamine), exclusively evoked an increase in I(sc), whereas the histamine H(2) agonist, amthamine, evoked only a decrease in I(sc) suggesting that stimulation of different types of histamine receptors is responsible for the two phases of the response evoked by native histamine. Histamine induces the opening of glibenclamide-sensitive Cl(-) channels and of charybdotoxin-sensitive K(+) channels in the apical membrane as demonstrated by experiments at basolaterally depolarized epithelia. A further action site is the basolateral membrane, because histamine stimulates a charybdotoxin- and tetrapentylammonium-sensitive K(+) conductance in this membrane as observed in tissues, in which the apical membrane was permeabilized with an ionophore, nystatin. The increase in I(sc) evoked by histamine was blocked after depletion of intracellular Ca(2+) stores with cyclopiazonic acid and after blockade of inositol 1,4,5-trisphosphate (IP(3)) receptors, suggesting a release of stored Ca(2+). This was confirmed by the observation that the histamine H(1) agonist TMPH induced an increase in the fura-2 ratio signal of epithelial cells within isolated colonic crypts. Consequently, the mediator histamine seems to stimulate both histamine H(1) and H(2) receptors, from which the former seems to be prominently involved in the induction of epithelial chloride secretion.