Na(+)-Ca2+ exchange in intact endothelium of rabbit cardiac valve.
A new method of measuring cytoplasmic free Ca2+ ([Ca2+]i) of individual intact cardiovascular endothelial cells by using imaging fluorescence microscopy was designed. Application of agonist to the aortic or pulmonary valve of the rabbit triggered an increase in [Ca2+]i, which depended on the existence of endothelium on the surface of the valve. Under resting conditions, sudden reversal of the Na+ gradient by substituting external Na+ with N-methyl D-glucamine (NMDG) resulted in a [Ca2+]i spike, which then returned toward the resting level. Increasing intracellular Na+ concentration ([Na+]i) by application of ouabain or monensin induced a sustained [Ca2+]i increase. Na+ substitution by NMDG during the agonist- or monensin-induced [Ca2+]i increase gave rise to a further [Ca2+]i spike, which subsequently declined to a level higher than that before removal of external Na+. A selective inhibitor of Na(+)-Ca2+ exchange, 3',4'-dichlorobenzamyl (DCB), abolished the transient [Ca2+]i increase induced by Na+ substitution, and Mg2+, an inorganic inhibitor of Na(+)-Ca2+ exchanger, markedly reduced this transient [Ca2+]i increase. On the other hand, the selective Na(+)-H+ exchanger blocker 5-(N,N-hexamethylene)amiloride (HMA) did not abolish the transient [Ca2+]i increase caused by Na+ substitution. In summary, decreasing the Na+ gradient of the endothelial cells through either receptor stimulation (agonist), Na(+)-K+ pump inhibition (ouabain), pretreatment with Na+ ionophore (monensin), or reversing the Na+ gradient through Na+ substitution (NMDG) all increased [Ca2+]i. This raised [Ca2+]i was antagonized by agents such as DCB or Mg2+, which are thought to inhibit Na(+)-Ca2+ exchange, but not by HMA, an inhibitor of Na(+)-H+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada.
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D000109:Acetylcholine / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004727:Endothelium / Q000378:metabolism*; D006351:Heart Valves / Q000378:metabolism*; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008536:Meglumine / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000032:analysis
D017923:Sodium-Hydrogen Exchangers; C057360:5-(N,N-hexamethylene)amiloride; D008536:Meglumine; D000584:Amiloride; D008094:Lithium; D012964:Sodium; D000109:Acetylcholine; D002118:Calcium