Differential Coronary Microvascular Exchange Responses to Adenosine: Roles of Receptor and Microvessel Subtypes

Abstract

Objective-To assess the role of adenosine receptors in the regulation of coronary microvascular permeability to porcine serum albumin ( ).Methods-Solute flux was measured in single perfused arterioles and venules isolated from pig hearts using fluorescent dye-labeled probes by microspectro-fluorometry. Messenger RNA, protein, and cellular distribution of adenosine receptors in arterioles and venules were analyzed by RT-PCR, immunoblot, and immunofluorescence.Results-Control venule (10.7 ± 4.8 × 10 −7 cm s −1 ) was greater than that of arterioles (6.4 ± 2.8 × 10 −7 cm · s −1 ; p <.05). Arteriolar decreased ( p <.05) with adenosine suffusion over the range from 10 −8 to 10 −5 M, while venular did not change. The nonselective A 1 and A 2 receptor antagonist, 8-(p-sulfophenyl) theophylline, blocked the adenosine-induced decrease in arteriolar . Messenger RNA for adenosine A 1 ,A 2A ,A 2B , and A 3 receptors was expressed in arterioles and venules. Protein for A 1 , A 2A , and A 2B , but not A 3 , was detected in both microvessel types and was further demonstrated on vascular endothelial cells. Conclusion-Arteriolardecreases with adenosine suffusion but not venular . Adenosine A 1 , A 2A , and A 2B receptors are expressed in both arterioles and venules. Selective receptor-linked cellular signaling mechanisms underlying the regulation of permeability remain to be determined. Keywords adenosine receptor; arteriole; heart; permeability; swine; venule In the heart the vasculature is critical for maintaining cardiac function via delivery of O 2 and nutrients, including free fatty acids carried on albumin, to the interstitial spaces around the myocardial cells and transport of metabolic by-products and hormones such as the natriuretic peptides away from the myocytes. Coronary exchange capacity depends on the surface area and permeability of all vessels available for exchange. Adenosine (ADO), a NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript metabolite of adenine nucleotides, is increased dramatically when an imbalance between oxygen supply and consumption exists under a variety of conditions including hypoxia, ischemia/reperfusion, and inflammation (4,61,62). Subsequently, ADO plays a myriad of important cardioprotective roles, including vasodilatation. Conventionally, it is assumed that permeability properties are either unchanged or affected insignificantly when coronary exchange capacity is assessed under the condition of constant surface area during ADOinduced maximal vasodilatation (37). However, evidence from studies with cultured endothelium (15,54,65), as well as conduit and microvascular vessels (5,12,35) showed that ADO influenced exchange, eliciting predominantly a decrease in permeability. It has been argued that findings from in vivo studies result primarily from a direct response of the endothelium to ADO combined with secondary effects of ADO on exchange mediated by hemodynamics, platelet, neutrophil, and/or mast cell functions.Recently, we modified the techniques for asse...

Adenosine A2A receptor modulation of juvenile female rat skeletal muscle microvessel permeability

“…The first result, contrary to expectation (43), was that basal permeability of venules was not higher than that of the arterioles. Indeed, this outcome is in contrast with that observed in other vascular beds (venular P s Ͼ arteriolar P s ) including adult (29,57) and juvenile porcine heart (24, 59) and skeletal muscles of adult male rat (48), mouse (48), guinea pig (43), and rabbit (50). The primary difference between the current study and those published previously is that the venous values are significantly lower than reported for other rodent skeletal muscle models (adult male) (57).…”

“…9), consistent with the proposal that microvessel barrier resistance by ADO was primarily mediated by the ADO A 2A receptor-adenylyl cyclase pathway. We also found that ADO A 2A receptors exist in arteriolar smooth muscle cells (57 ). Others have shown that A 2A receptors are expressed on platelets, neutrophils, and mast cells, all of which they are involved in anti-inflammatory activity, especially under ischemic conditions (35).…”

“…It is well known that, in skeletal muscle, ADO is an important local metabolic vasodilator (6,14,39). In addition to ADO having the capacity to regulate blood flow delivery, and hence exchange, by dilating feed arterioles, ADO has been shown recently to regulate the exchange of protein by mediating permeability changes in coronary microvessels (25,29,30,57).…”

“…Extraction of mRNA from single isolated arterioles and venules (ID Ͻ100 M, 1-2 mm in length) using paramagnetic oligo(dT) polystyrene beads [Dynabeads Oligo(dT) 25; Dynal, Carlsbad, CA] was described previously (57). In brief, individual isolated microvessels were homogenized in LiCl lysis buffer.…”

“…The expression of ADO receptor protein in arterioles and venules isolated from the juvenile female rat abdominal skeletal muscle was assessed by immunoblot analysis as described previously (57). In brief, each sample consisted of one to two arterioles or venules (ID Ͻ100 m, 1 mm in length) homogenized in solubilization buffer [50 mM Tris ⅐ HCl (pH ϭ 7.4), 6 M urea, and 2% SDS (vol/vol) (47)]; the cell lysates were subjected to SDS-PAGE [10% (wt/vol) for A 2A and A2B, 12% for A1 and A3], and protein was transferred to a polyvinylidene difluoride (PVDF) membrane.…”