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Transport and Metabolism of Adenosine and its Metabolites in Capillary Endothelial Cells of Guinea Pig Hearts
Author(s) -
Liu Aiping,
Bassingthwaighte James B.
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.706.10
Subject(s) - hypoxanthine , adenosine , inosine , xanthine , chemistry , metabolism , metabolite , biochemistry , purine , bolus (digestion) , medicine , enzyme
Adenosine (Ado) plays an important role in cardioprotection during ischemia by enhancing coronary flow through binding to purinoceptors on smooth muscle cells (SMC), and by preserving nucleotide pools through purine salvage in cardiomyocytes (MC). However, two questions impede our understanding of the mechanism by which Ado acts on MCs or SMCs: (1) how much Ado reaches cardiomyoctyes or SMC when EC avidly take‐up Ado from blood stream and interstitium? and (2) how much Ado degrades to uric acid (UA), or is salvaged back into cellular pools, mainly ATP? Our goal here is to quantify the fluxes of Ado and its metabolites in ECs. The multiple‐indicator‐dilution technique (MID) was used to measure the capillary transport and metabolism of Ado and metabolites in isolated, Krebs‐Ringer perfusated guinea pig hearts. Radiolabeled [ 14 C]‐ adenosine, or inosine, or hypoxanthine, or xanthine was injected with [ 131 I]‐albumin (intravascular reference solute) and [ 3 H] AraH or L‐[ 3 H] glucose (extracellular references) as a bolus into the coronary flow; venous outflow dilution curves of the injectate and its metabolites were quantified with HPLC and LS counting. The permeabilities of each solute (via interendothelial clefts, PSg, trans‐endothelial membrane, PSecl, trans‐cardiomyocytes PSpc) and the metabolism in ECs and MCs were estimated by fitting the MID curves with a general convection‐diffusion‐exchange‐reaction model, Gentex. Results are: Intracellular sequestration of injected Ado is high compared to its metabolites (~60% of Ado vs. ~50% of Ino). Similarly, PSecl is higher for Ado than metabolites, INo>Hx>Xa> UA (Ado:1.9±0.7 vs. Ino:1.7±0.5 vs. Hx: 0.5±0.1 ml·min −1 ·g −1 ). The low permeabilities help to retain purine in the cells. Plasma injectate Ado that enters ECs is estimated to be ~50% oxidized to UA, ~50% retained; Hx is ~67% oxidized, ~23% retained, both presumably incorporated into nucleotide pools. Thus ECs actively participate in purine salvage via both Ado and Hx. Uncertainty for EC parameters is much smaller than for MC. Having well‐defined parameters for permeabilities and metabolism for Ado and its metabolites in ECs is an essential step toward understanding the fate of endogenous Ado generated from cardiomyocytes during ischemia and reperfusion. Support or Funding Information Our study was supported by NIH research grant U01HL122199. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .