Effects of propionate and ammonium on contractions produced by sodium removal in human internal mammary artery and saphenous vein

Effects of propionate and ammonium on contractions produced by Na+ removal (0-Na+ contraction, replaced with N-methyl-D-glucamine) were studied and compared with those produced by 60 mM K+ in muscle strips isolated from human internal mammary artery (IMA) and saphenous vein (SV), clinically used as bypass vessels. Contractions induced by 60 mM K+ (60-K+ contractions) were similar in both vessels, 0-Na+ contraction was significantly larger in the vein than in the artery, Neither 60-K+ nor 0-Na+ contractions were significantly affected by N-G-nitro-L-arginine (30 mu M) or phenoxybenzamine (1 mu M). Ouabain (2 mu M) slowly potentiated 0-Na+ contractions and the 3rd contraction produced 60 min after ouabain application was 291+/-36% in the artery and 184+/-41% of the control (n=10) in the vein, Propionate (20 mM) potentiated 60-K+ contraction more strongly in the vein than in the artery, but potentiation of 0-Na+ contraction was greater in the artery than in the vein, On the other hand, ammonium (20 mM) inhibited 60-K+ contractions more strongly in the artery than the vein, whereas inhibition of 0-Na+ contraction was stronger in the vein. 0-Na+ contraction is likely to be produced by an Na+-Ca2+ exchange mechanism, and the effects of propionate and ammonium are considered to be mediated by intracellular acidification and alkalinization, respectively, It is speculated that an Na+-H+ exchange may also be involved in 0-Na+ contraction and that SV has slightly lower pH(i) than IMA.