NS309 restores EDHF-type relaxation in mesenteric small arteries from type 2 diabetic ZDF rats

Background and purpose: The endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in mesenteric small arteries from 21 week old Zucker lean (ZL) and Zucker diabetic fatty (ZDF) rats was investigated using (6,7-dichloro-1H-indole-2,3-dione 3-oxime) (NS309), a potent activator of small-conductance, calcium-activated potassium channel (SKCa) and intermediate-conductance, calcium-activated potassium channel (IKCa). Experimental approach: In the presence of inhibitors of cyclooxygenase and nitric oxide synthase [indomethacin and N-omega-nitro-L-arginine methyl ester (l-NAME), respectively], acetylcholine (ACh)-induced hyperpolarization and EDHF-type relaxation were investigated under isometric conditions in the wire myograph using 0.5 and 1 mu M NS309 and/or selective blockers of SKCa and IKCa channels. Membrane potential was recorded with glass microelectrodes, and changes in the intracellular calcium concentration of endothelial cells were visualized by confocal microscopy. SKCa expression was assessed by Western blotting. Key results: In arteries from ZDF rats, ACh-induced relaxation and membrane hyperpolarization were attenuated and, compared with arteries from ZL rats, NS309 was less potent at causing relaxation. Incubation with 0.5 mu M NS309 did not increase ACh-induced relaxation in arteries from ZDF rats significantly. However, 1 mu M NS309 restored it (both in the absence and in the presence of indomethacin and l-NAME) without changing endothelial intracellular calcium concentration. The restored EDHF-type relaxation was more sensitive to TRAM-34 (1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole) (1 mu M) than to apamin. Expression of the SKCa channel was unaltered. Conclusions and implications: The attenuated EDHF-type relaxation in mesenteric small arteries from ZDF rats can be restored by NS309 without changes in the intracellular calcium concentration of endothelial cells. These results may have clinical implications for the treatment of endothelial dysfunction in overweight type 2 diabetic patients. British Journal of Pharmacology (2010) 159, 154-165; doi:10.1111/j.1476-5381.2009.00525.x; published online 10 December 2009