Basal and adenosine-mediated protein flux from isolated coronary arterioles

We have developed a new method to quantify solute flux per unit surface area and concentration gradient (J(s)/S Delta C) from arterioles isolated from pig hearts. The apparent permeability (P-s) was assessed from measurements of J(s)/S Delta C for two proteins, alpha-lactalbumin (alpha-lactalb) and porcine serum albumin (PSA), labeled with the fluorescent dye tetramethylrhodamine isothiocyanate at a mean hydrostatic pressure of 16 +/- 1 cmH(2)O. P-s for alpha-lactalb (P-s(alpha-lactalb)) was 16.5 +/- 4.6 X 10(-7) cm/s (mean +/- SE, N = 8 pigs), a value significantly higher than P-s for PSA (P-s(PSA)) (7.1 +/- 1.4 X 10(-7) cm/s, N = 11 pigs, P < 0.05). Suffusion of the arterioles (44 +/- 10 mu m diam, n = 48 arterioles) with 10(-5) M adenosine resulted in a 35% decrease in P-s(alpha-lactalb) and 29% decrease in P-s(PSA). Data from the present study are consistent with adenosine altering arteriole J(s) independently from its ability to change arteriolar caliber. One implication of these results is that changes in coronary exchange capacity reflect not only changes in flow through, but also solute permeation from, the microvasculature.