Altered basal and adenosine‐mediated protein flux from coronary arterioles isolated from exercise‐trained pigs

Solute flux per unit surface area and concentration gradient, (JS/SΔC), was quantified in arterioles isolated from hearts of sedentary (SED) and exercise‐trained (EX) female Yucatan Miniature Swine. Apparent permeability (PS) was assessed from measures of JS/SΔC for two proteins, α‐lactalbumin (α‐lact) and porcine serum albumin (PSA), under basal conditions and following 5 min suffusion with 10−5M adenosine (ADO). Both proteins were labelled with the fluorescent dye tetramethyl rhodamine isothiocyanate. Basal Ps to α‐lact differed with exercise training ((Pα‐lacts)SED=5.2±1.8 (median±median absolute deviation (MAD), n=9 pigs) versus (Pα‐lacts)EX=7.4±1.1×10−7 cm s−1, n=9, P<0.05). For the larger protein PSA, basal Ps did not change with training ((PPSAs)SED=5.0±1.6, N=11 vs. (PPSAs)EX=4.1±1.2×10−7 cm s−1, N=11). Suffusion of the arterioles (33±4 μm diameter, n=18 vessels) from SED hearts (n=14) with 10−5M ADO decreased Pα‐lacts 15±8% relative to control and was without effect on PPSAs. By contrast, in arterioles (39±4 μm diameter, n=22 vessels) from EX hearts (n=14), ADO increased Pα‐lacts and PPSAs by 32 and 65% respectively, indicating that receptor‐mediated changes in permeability were also sensitive to exercise training. These data demonstrate that, for coronary arterioles, permeability to macromolecules adapts to exercise training. The adaptive mechanisms may involve more than one structural component of the vessel wall as the changes in permeability were size‐dependent.