Alignment of amino acid sequences of the human histamine H1- and H2-receptors. Residues that are identical in the two sequences are shown in bold. Lines show the putative transmembrane spanning domains.
Operational characteristics of histamine receptors
Most smooth muscle, endothelial cells, adrenal medulla, heart, CNS
Smooth muscle contraction, stimulation of NO formation, endothelial cell contraction, increased vascular permeability, stimulation of hormone release, negative inotropism, depolarization (block of leak potassium current) and increased neuronal firing, inositol phospholipid hydrolysis and calcium mobilization, hyperpolarization by Ca2+-dependent potassium current
Stimulation of gastric acid secretion, smooth muscle relaxation, stimulation of adenylyl cyclase, positive chronotropic and inotropic effects on cardiac muscle, decreased firing rate, hyperpolarization or facilitation of signal transduction in CNS, block of Ca2+-dependent potassium conductance (I AHP, accommodation of firing, after-hyperpolarization), increase of hyperpolarization-activated current, inhibition of lymphocyte function
Values determined from guinea pig ileum contraction (H1), guinea pig atrium (chronotropic stimulation, H2), and inhibition of K+-stimulated histamine release from rat cerebral cortical slices (H3), or inhibition of electrically stimulated contraction of guinea pig ileum (H3). n.d., not determined.
Measurements were made of H2-mediated adenylyl cyclase activity in homogenates of guinea pig hippocampus, impromidine-stimulated cyclic AMP accumulation in guinea pig hippocampal slices, and of H2-mediated cyclic AMP accumulation in dissociated hippocampal tissue. n.d., not determined.