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We conclude that JC-1 is the optimal dye to use when measuring Deltapsim in cardiomyocytes.

1 The receptor subtype and mechanisms underlying relaxation to adenosine were examined in human isolated small coronary arteries contracted with the thromboxane A 2 mimetic, 1,5,5-hydroxy11a, 9a-(epoxymethano)prosta-5Z, 13E-dienoic acid (U46619) to approximately 50% of their maximum contraction to K + (125 mM) depolarization (F max ). Relaxations were normalized as percentages of the 50% F max contraction. 2 Adenosine caused concentration-dependent relaxations (pEC 50 , 5.95+0.20; maximum relaxation (R max ), 96.7+1.4%) that were una ected by either combined treatment with the nitric oxide inhibitors, N G -nitro-L-arginine (L-NOARG; 100 mM) and oxyhaemoglobin (HbO; 20 mM) or the ATP-dependent K + channel (K ATP ) inhibitor, glibenclamide (10 mM). The pEC 50 but not R max to adenosine was signi®cantly reduced by high extracellular K + (30 mM). Relaxations to the adenylate cyclase activator, forskolin, however, were una ected by high K + (30 mM). . By contrast, the A 1 -selective antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) had no e ect on pEC 50 or R max to adenosine. 5 These results suggest that A 2B receptors mediate relaxation to adenosine in human small coronary arteries which is independent of NO but dependent in part on a K + -sensitive mechanism.

1 The eects of the nitric oxide (NO) synthase inhibitor, N G -nitro-L-arginine (L-NOARG), the NO scavenger, oxyhaemoglobin (HbO) and high extracellular K + upon endothelium-dependent relaxation to bradykinin were investigated in human isolated small coronary arteries. 2 Endothelium-dependent relaxations to bradykinin were compared in vessels contracted to *50% of their maximum contraction to 124 mM KCl Krebs solution, regardless of treatments, with the thromboxane A 2 mimetic, U46619 and acetylcholine. All relaxations were expressed as percentage reversal of the initial level of active force. 3 L-NOARG (100 mM) caused a small but signi®cant, 12% (P50.01), decrease in the maximum relaxation (R max : 91.5+5.4%) to bradykinin but did not signi®cantly aect the sensitivity (pEC 50 : 8.08+0.17). Increasing the concentration of L-NOARG to 300 mM had no further eect on the pEC 50 or R max to bradykinin. HbO (20 mM) and a combination of HbO (20 mM) and L-NOARG (100 mM) reduced R max to bradykinin by 58% (P50.05) and 54% (P50.05), respectively. HbO (20 mM) and L-NOARG (100 mM, combined but not HbO (20 mM) alone, caused a signi®cant 11 fold (P50.05) decrease in sensitivitiy to bradykinin. HbO (20 mM) decreased the sensitivity to the endothelium-independent NO donor, S-nitroso-N-acetylpenicillamine (SNAP), approximately 17 fold (P50.05). 4 Raising the extracellular concentration of K + isotonically to 30 mM, reduced the R max to bradykinin from 96.6+3.1% to 43.9+10.1% (P50.01) with no signi®cant change in sensitivity. A combination of HbO, L-NOARG and high K + (30 mM) abolished the response to bradykinin. High K + did not change either the sensitivity or maximum relaxation to SNAP. 5 In conclusion, L-NOARG does not completely inhibit endothelial cell NO synthesis in human isolated small coronary arteries. By comparison, HbO appeared to block all the eects of NO in this tissue and revealed that most of the relaxation to bradykinin was due to NO. The non-NO -dependent relaxation to bradykinin in the human isolated small coronary arteries appeared to be mediated by a K + -sensitive vasodilator mechanism, possibly endothelium-derived hyperpolarizing factor (EDHF).