Endothelium-derived hyperpolarizing factor and potassium use different mechanisms to induce relaxation of human subcutaneous resistance arteries

This investigation examined the hypothesis that release of K+ accounts for EDHF activity by comparing relaxant responses produced by ACh and KCl in human subcutaneous resistance arteries. 2 Resistance arteries (internal diameter 244 +/- 12 mum, n = 48) from human subcutaneous fat biopsies were suspended in a wire myograph. Cumulative concentration-response curves were obtained for ACh (10(-9)-3 x 10(-5) M) and KCI (2.5-25 mM) following contraction with noradrenaline (NA; 0.1-3 muM). 3 ACh (E-max 99.07 +/-9.61%; -LogIC(50) 7.03 +/-0.22; n=9) and KCl (E-max 74.14 +/-5.61%; -LogIC(50) 2.12 +/-0.07 n= 10)-induced relaxations were attenuated (P<0.0001) by removal of the endothelium (E-max 8.21<plus/minus>5.39% and 11.56 +/-8.49%, respectively; n=6-7). 4 Indomethacin (10 muM) did not alter ACh-induced relaxation whereas L-NOARG (100 muM) reduced this response (E-max 61.7 +/-3.4%, P <0.0001; n=6). The combination of ChTx (50 nM) and apamin (30 nM) attenuated the L-NOARG-insensitive component of ACh-induced relaxation (E-max: 15.2 +/- 10.5%, P <0.002, n=6) although these arteries retained the ability to relax in response to 100 muM SIN-I (E-max 127.6 +/- 13.0%, n=3). Exposure to BaCl2 (30 muM) and Ouabain (1 mM) did not attenuate the L-NOARG resistant component of ACh-mediated relaxation (E-max 76.09 +/-8.92, P=0.16; n=5). 5 KCl-mediated relaxation was unaffected by L-NOARG + indomethacin (E-max; 68.1 +/-5.6%, P=0.33; n=5) or the combination of L-NOARG/indomethacin/ChTx/apamin (E-max; 86.61 +/- 14.02%, P=0.35; n= 6). In contrast, the combination of L-NOARG, indomethacin, ouabain and BaCl2 abolished this response (E-max, 5.67 +/-2.59%, P<0.0001, n=6). 6 The characteristics of KCI-mediated relaxation differed from those of the nitric oxide/prostaglandin-independent component of the response to ACh, and were endothelium-dependent, indicating that KI does not act as an EDHF in human subcutaneous resistance arteries.