Translocation of AT₁- and AT₂-Receptors by Higher Concentrations of Angiotensin II in the Smooth Muscle Cells of Rat Internal Anal Sphincter

Abstract

Previous studies have reported bimodal effects by angiotensin II (Ang II) in the rat internal anal sphincter (IAS), a concentrationdependent contraction (at lower concentrations) and relaxation (at higher concentrations). The experiments suggest the abovementioned responses are the result of Ang II subtype I receptor(s) (AT 1 -R) and subtype II receptor(s) (AT 2 -R) activation, respectively. These studies determined the role and mechanism of AT 2 -R-induced relaxation of the smooth muscle cells (SMCs) from the IAS in response to Ang II. Laser confocal microscopy showed that in the basal state, the AT 1 -Rs reside in the plasma membrane, whereas AT 2 -Rs are present in the cytosol. Higher concentrations of Ang II caused movement of AT 1 -R and AT 2 -R in opposite directions to the cytosol and the membrane, respectively. Losartan (AT 1 -R antagonist) but not S-(ϩ)-1-([4-(d-,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid (PD123319; AT 2 -R antagonist) selectively inhibited these movements. These results are based on biotinylation assays, confocal images, and Western blot analyses of the densities of AT 1 -Rs and AT 2 -Rs in the plasma membrane versus cytosolic fractions of the IAS SMCs. Ang II in higher concentrations did not change the total contents of Ang II receptors. These data combined with the functional data using measurements of IAS SMC lengths suggest that internalization of AT 1 -R and externalization of AT 2 -R may be responsible for the activation of the AT 2 -R, which leads to the relaxation of the IAS with higher concentrations of Ang II.

Adapter proteins and promoter regulation of the angiotensin AT2 receptor — implications for cardiac pathophysiology

“…In addition, our observations regarding the functional role of ATBP -i.e., a protein necessary for transport as well as function of the AT 2 receptor -are consistent with two recent publications. Work of de Godoy and Rattan indicates that the externalisation of the AT 2 receptor from an intracellular localisation to the plasma membrane may be responsible for receptor activation 43 which is consistent with observations of Miura et al suggesting that AT 2 receptor translocation in the cell membrane is necessary for cell signalling. 30 Apart from the signal transduction cascades downstream of the AT 2 receptor linked to direct physical interactions, our group was able to show that AT 2 receptor activation regulates the mRNA level of the zinc finger homoeodomain enhancerbinding protein (Zfhep).…”

Expression and Distribution of NADPH Oxidase Isoforms in Human Myometrium—Role in Angiotensin II-induced Hypertrophy1

“…Vascular prostaglandin synthesis is induced by Ang II [56], whereas prostaglandin E2 has been found to counteract the effect of Ang II on activation of NADPH oxidase and vasoconstriction in a mouse model [57]. In addition, high Ang II concentrations may result in agonist-induced receptor internalization and/or desensitization [58,59]. This may also explain the moderate effect of Ang II on myometrium protein synthesis/hypertrophy seen in the current model.…”

The angiotensin II type 2 receptor and the gastrointestinal tract

“…In an elegant follow-up study on rat internal anal sphincter, de Godoy and Rattan demonstrated that internalisation of AT 1 receptors and externalisation of AT 2 receptors may be responsible for the activation of the AT 2 receptors, which leads to the relaxation at higher concentrations of Ang II. 18 As the internalisation/externalisation behaviour depends on Ang II receptor activation, it is an important issue to consider when judging effects of Ang II and related receptor ligands. It is obvious that the role of AT 2 receptors on myenteric neurons in the GI tract needs further investigation.…”