Platelet-activating factor increases endothelial [Ca2+]i and NO production in individually perfused intact microvessels.
We have demonstrated that inhibition of NO synthase (NOS) in endothelial cells by either the NOS inhibitor N(omega)-monomethyl-l-arginine (l-NMMA) or the internalization of caveolin-1 scaffolding domain attenuated platelet-activating factor (PAF)-induced increases in microvessel permeability (Am J Physiol Heart Circ Physiol 286: H195-H201, 2004) indicating the involvement of an NO-dependent signaling pathway. To investigate whether an increase in endothelial cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) is the initiating event and Ca(2+)-dependent NO production is crucial for permeability increases, PAF (10 nM)-induced changes in endothelial [Ca(2+)](i) and NO production were measured in individually perfused rat mesenteric venular microvessels via fluorescence microscopy. When venular microvessels were exposed to PAF, endothelial [Ca(2+)](i) increased from 69 +/- 8 nM to a peak value of 374 +/- 26 nM within 3 min and then declined to a sustained level at 190 +/- 12 nM after 15 min. Inhibition of NOS did not modify PAF-induced increases in endothelial [Ca(2+)](i). PAF-induced NO production was visualized and quantified at cellular levels in individually perfused microvessels using 4,5-diaminofluorescein diacetate and fluorescence imaging. Increased fluorescence intensity (FI), which is an indication of increased NO production, occurred in 75 +/- 7% of endothelial cells in each vessel. The mean maximum FI increase was 140 +/- 7% of baseline value. This increased FI was abolished by pretreatment of the vessel with l-NMMA and attenuated in the absence of extracellular Ca(2+). These results provide direct evidence from intact microvessels that increased endothelial [Ca(2+)](i) is the initial signal that activates endothelial NOS, and the subsequent increased NO production contributes to PAF-induced increases in microvessel permeability.
Zhu
Longkun
L
Dept. of Physiology and Pharmacology, School of Medicine, Health Sciences Center, West Virginia Univ., Morgantown, WV 26506-9229, USA.
He
Pingnian
P
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D008642:Mesenteric Veins; D008833:Microcirculation / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000096:biosynthesis*; D009599:Nitroprusside / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000494:pharmacology*; D051381:Rats; D014699:Venules / Q000187:drug effects / Q000502:physiology; D019323:omega-N-Methylarginine / Q000494:pharmacology
D010972:Platelet Activating Factor; D009599:Nitroprusside; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D002118:Calcium