Adenosine A_2A receptor modulation of juvenile female rat skeletal muscle microvessel permeability

Abstract

Wang, Jianjie, and Virginia H. Huxley. Adenosine A2A receptor modulation of juvenile female rat skeletal muscle microvessel permeability. Am J Physiol Heart Circ Physiol 291: H3094 -H3105, 2006. First published June 30, 2006 doi:10.1152/ajpheart.00526.2006Little is known of the regulation of skeletal muscle microvascular exchange under resting or stimulating conditions. Adenosine (ADO) levels in skeletal muscle increase during physiological (exercise) and pathological (hypoxia, inflammation, and ischemia) conditions. Later stages of these pathologies are characterized by the loss of vascular barrier integrity. This study focused on determining which ADO receptor mediates the robust reduction in microvessel permeability to rat serum albumin (P s RSA ) observed in juvenile female rats. In microvessels isolated from abdominal skeletal muscle, ADO suffusion induced a concentration-dependent reduction in arteriolar [log(IC 50) RT-PCR and immunoblot analysis demonstrated mRNA and protein expression of ADO A1, A2A, A2B, and A3 receptors in both vessel types, and immunofluorescence assay revealed expression of the four subtype receptors in the microvascular walls (endothelium and smooth muscle). P s RSA responses of arterioles and venules to ADO were blocked by 8-(p-sulphophenyl)theophylline, a nonselective A1 and A2 antagonist. An A2A agonist, CGS21680, was more potent than the A1 agonist, cyclopentyladenosine, or the most-selective A2B agonist, 5Ј-(N-ethylcarboxamido)adenosine. The ability of CGS21680 or ADO to reduce P s RSA was abolished by the A2A antagonist, ZM241385. An adenylyl cyclase inhibitor, SQ22536, blocked the permeability response to ADO. In aggregate, these results demonstrate that, in juvenile females (before the production of the reproductive hormones), ADO enhances skeletal muscle arteriole and venule barrier function predominantly via A2A receptors using activation of adenylyl cyclase-signaling mechanisms. adenosine receptors; albumin; microvascular exchange; arteriole; venule SKELETAL MUSCLE MICROVESSELS have a large capacity to vasodilate and increase blood flow, thereby increasing oxygen and nutrient supply during exercise (7). During whole body dynamic exercise at maximal oxygen consumption, skeletal muscle receives 85-90% of cardiac output (11) compared with 20% at rest. Adenosine (ADO), a ubiquitous adenine nucleoside, was shown to be a key vasodilator in skeletal muscles under physiological and pathophysiological conditions including hypoxia (5), ischemia, and muscle contraction (8,22,23,34). Furthermore, ADO was found, from measures of permeability-surface area product (13), to increase skeletal muscle microvasculature blood-tissue exchange, an increase believed to be secondary to the increased exchange surface area downstream from the arterioles dilating in response to ADO (1,6,7,14). It is unclear, however, whether ADO itself could modulate skeletal muscle permeability. The feedback mechanism of skeletal muscle myocyte contraction resulting in ADO production, which can regulate blood flo...

Sphingosine-1-phosphate prevents permeability increases via activation of endothelial sphingosine-1-phosphate receptor 1 in rat venules

“…This phenomenon does not appear unique for S1P. Similar observations have also been reported in adenosine receptor-mediated permeability responses (39).…”

Adaptation of coronary microvascular exchange in arterioles and venules to exercise training and a role for sex in determining permeability responses

“…25), in isolated coronary venules from SED males (this study and Ref. 25) and also in skeletal muscle arterioles and venules isolated from juvenile female rats (60). We note that the AV gradient observed by Wang and Huxley (60) in the skeletal muscle microvessels under basal conditions was abolished in the presence of ADO.…”

Intrinsic sex-specific differences in microvascular endothelial cell phosphodiesterases

“…EC sex-typing (XY vs. XX) was determined by a gene of SRY (sex-determining region Y) on the Y chromosome using RT-PCR assay described previously (47). Primers for specific SRY (Gene Bank, NM_012772) were as follows: forward 5=-62 GCAAGTTGGCTCAACAGA 79 -3=; reverse 5=-442 GTT-TCTGCTGTAGTGGGTA 424 -3=.…”

“…Localization of PDE in skeletal muscle microvessels was assessed by immunofluorescence and confocal laserscanning microscopy, described previously (47). In brief, abdominal skeletal muscles were embedded in OCT compound (Sakura Finetek, Torrance, CA) and then sectioned using cryostat.…”