Endothelium-derived hyperpolarizing factor but not NO reduces smooth muscle Ca2+ during acetylcholine-induced dilation of microvessels.
1. We hypothesized that nitric oxide (NO) and the endothelium-dependent hyperpolarizing factor (EDHF) may dilate microvessels by different cellular mechanisms, namely Ca2+-desensitization versus decrease in intracellular free calcium. 2. Effects of acetylcholine (ACh) and the NO donors sodium nitroprusside (SNP, 0.1 - 10 micromol l(-1)) and S-Nitroso-N-acetyl-D, L-penicillamine (SNAP, 0.01 - 10 micromol l-1) on intracellular calcium ([Ca2+]i, fura 2) and vascular diameter (videomicroscopy) were studied in isolated resistance arteries from hamster gracilis muscle (194+/-12 microm) pretreated with indomethacin and norepinephrine. Membrane potential changes were determined using 1, 3-dibutylbarbituric acid trimethineoxonol (DiBAC4(3)). 3. ACh (0.1 and 1 micromol l-1)-induced dilations were associated with a [Ca2+]i decrease (by 13+/-3 and 32+/-4%) and hyperpolarization of vascular smooth muscle (VSM, by 12+/-1% at 1 micromol l-1 ACh). Nomega-nitro-L-arginine (L-NA, 30 micromol l(-1)) partially inhibited the dilation but did not affect VSM [Ca2+]i decreases or hyperpolarization. In contrast, the KCa channel inhibitors tetrabutylammonium (TBA, 1 mmol l(-1)) and charybdotoxin (ChTX, 1 micromol l(-1)) abolished the ACh-induced [Ca2+]i decrease and the hyperpolarization in VSM while a significant dilation remained (25 and 40%). This remaining dilation was abolished by L-NA. ChTX did not affect [Ca2+]i increase and hyperpolarization in endothelial cells. SNP- or SNAP-induced dilations were not associated with decreases in VSM [Ca2+]i or hyperpolarization although minor transient decreases in VSM [Ca2+]i were observed at high concentrations. 4. These data suggest that ACh-induced dilations in microvessels are predominantly mediated by a factor different from NO and PGI2, presumably EDHF. EDHF exerts dilation by activation of KCa channels and a subsequent decrease in VSM [Ca2+]i, NO dilates the microvessels in a calcium-independent manner.
Bolz
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SS
Institute of Physiology, Ludwig-Maximilians-University Munich, Pettenkoferstrasse 12, D-80336 Munich, Germany. bolz@lrz.uni-muenchen .de
de Wit
C
C
Pohl
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U
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001158:Arteries; D001685:Biological Factors / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D006224:Cricetinae; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D015736:Felodipine / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008647:Mesocricetus; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D014664:Vasodilation / Q000187:drug effects*
D001685:Biological Factors; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D016861:Cyclooxygenase Inhibitors; D020030:Nitric Oxide Donors; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000109:Acetylcholine; D015736:Felodipine; D011188:Potassium; D002118:Calcium