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. Resistance arteries (internal diameter 244±12 μm, n=48) from human subcutaneous fat biopsies were suspended in a wire myograph. Cumulative concentration-response curves were obtained for ACh (10−9 – 3×10−5 M) and KCl (2.5 – 25 mM) following contraction with noradrenaline (NA; 0.1 – 3 μM). ACh (Emax 99.07±9.61%; −LogIC50 7.03±0.22; n=9) and KCl (Emax 74.14±5.61%; −LogIC50 2.12±0.07; n=10)-induced relaxations were attenuated (P<0.0001) by removal of the endothelium (Emax 8.21±5.39% and 11.56±8.49%, respectively; n=6 – 7). Indomethacin (10 μM) did not alter ACh-induced relaxation whereas L-NOARG (100 μM) reduced this response (Emax 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 (Emax: 15.2±10.5%, P<0.002, n=6) although these arteries retained the ability to relax in response to 100 μM SIN-1 (Emax 127.6±13.0%, n=3). Exposure to BaCl2 (30 μM) and Ouabain (1 mM) did not attenuate the L-NOARG resistant component of ACh-mediated relaxation (Emax, 76.09±8.92, P=0.16; n=5). KCl-mediated relaxation was unaffected by L-NOARG+indomethacin (Emax; 68.1±5.6%, P=0.33; n=5) or the combination of L-NOARG/indomethacin/ChTx/apamin (Emax; 86.61±14.02%, P=0.35; n=6). In contrast, the combination of L-NOARG, indomethacin, ouabain and BaCl2 abolished this response (Emax, 5.67±2.59%, P<0.0001, n=6). The characteristics of KCl-mediated relaxation differed from those of the nitric oxide/prostaglandin-independent component of the response to ACh, and were endothelium-dependent, indicating that K+ does not act as an EDHF in human subcutaneous resistance arteries. British Journal of Pharmacology (2001) 133, 902–908; doi:10.1038/sj.bjp.0704143