Detection of La3+ influx in ventricular cells by indo-1 fluorescence.
We exposed indo-1-loaded cultured embryonic chick ventricular cells to 0.03-1.0 mM extracellular lanthanum concentration ([La3+]o) and simultaneously measured cell contractile motion and the 410/480 nm fluorescence intensity ratio. After exposure to La3+, ventricular cells stopped contracting and relaxed within seconds, and the 410/480 fluorescence ratio increased. The increase in the 410/480 signal was related to [La3+]o but was not affected by short exposures to zero extracellular calcium concentration ([Ca2+]o) or caffeine, suggesting that the fluorescence was not caused by a La3+-induced increase in intracellular calcium concentration ([Ca2+]i) but rather to increased intracellular lanthanum concentration ([La3+]i). In vitro studies confirmed that indo-1 fluorescence was sensitive to La3+. The increase in [La3+]i in 0.1 mM [La3+]o was directly related to intracellular sodium concentration ([Na+]i), suggesting that La3+ entered cells via Na+-La3+ exchange. In contrast to ventricular cells, which have a functionally distinct Na+-Ca2+ exchange system, exposure of indo-1-loaded cultured bovine endothelial cells to La3+ failed to produce an increase in [La3+]i. These results indicate that exposure of ventricular cells to 0.1-1.0 mM [La3+]o results in a [La3+]i greater than 250 nM within 1 min. Therefore, changes in myocardial 45Ca2+ fluxes and contents induced by La3+ cannot be ascribed solely to extracellular La3+ effects.
Peeters
G A
GA
Department of Medicine, University of Utah, Salt Lake City 84132.
Kohmoto
O
O
Barry
W H
WH
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D005456:Fluorescent Dyes; D007211:Indoles; D007811:Lanthanum / Q000378:metabolism* / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D005456:Fluorescent Dyes; D007211:Indoles; D002110:Caffeine; D007811:Lanthanum; D012964:Sodium; C048960:indo-1; D002118:Calcium