Affiliation:
1. From the Department of Pharmacology and Therapeutics, The University of British Columbia, Vancouver, Canada.
Abstract
Abstract
A new method of measuring cytoplasmic free Ca
2+
([Ca
2+
]
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 [Ca
2+
]
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 [Ca
2+
]
i
spike, which then returned toward the resting level. Increasing intracellular Na
+
concentration ([Na
+
]
i
) by application of ouabain or monensin induced a sustained [Ca
2+
]
i
increase. Na
+
substitution by NMDG during the agonist- or monensin-induced [Ca
2+
]
i
increase gave rise to a further [Ca
2+
]
i
spike, which subsequently declined to a level higher than that before removal of external Na
+
. A selective inhibitor of Na
+
-Ca
2+
exchange, 3′,4′-dichlorobenzamyl (DCB), abolished the transient [Ca
2+
]
i
increase induced by Na
+
substitution, and Mg
2+
, an inorganic inhibitor of Na
+
-Ca
2+
exchanger, markedly reduced this transient [Ca
2+
]
i
increase. On the other hand, the selective Na
+
-H
+
exchanger blocker 5-(
N,N
-hexamethylene)amiloride (HMA) did not abolish the transient [Ca
2+
]
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 [Ca
2+
]
i
. This raised [Ca
2+
]
i
was antagonized by agents such as DCB or Mg
2+
, which are thought to inhibit Na
+
-Ca
2+
exchange, but not by HMA, an inhibitor of Na
+
-H
+
exchange. Taken together, these results strongly imply the presence of Na
+
-Ca
2+
exchange as a viable mechanism for Ca
2+
transport in intact cardiovascular endothelium and that the Ca
2+
entry component is enhanced when [Na
+
]
i
is elevated.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Cited by
40 articles.
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