Membrane potential as a modulator of the free intracellular Ca2+ concentration in agonist-activated endothelial cells.
We have used combined patch clamp and fura-2 fluorescence to elucidate the role of membrane potential in the regulation of the cytosolic Ca2+ concentration ([Ca2+]i) in a human umbilical vein derived endothelial cell-line, EA.hy926 (EA cells) stimulated with vasoactive agonists, such as ATP, histamine and bradykinin. This stimulation caused hyperpolarization and sustained Ca2+ plateau in nonclamped cells. Clamping agonist-stimulated cells at negative potentials enhanced the amplitude of this plateau, whereas it was smaller at more depolarized potentials, indicating that Ca2+ influx follows its driving force. Depolarization of the membrane by increasing extracellular K+ or by applying charybdotoxin, a blocker of big conductance Ca2+-dependent K+ channels during agonist stimulation diminished the plateau rise in [Ca2+]i. It is concluded that the membrane potential is an efficient regulator of Ca2+ influx during the plateau phase of agonist-mediated Ca2+ signals. In addition, the modulating effects on Ca2+ signals should be interpreted with caution if the membrane potential of the cells is not controlled.
Kamouchi
M
M
Laboratorium voor Fysiologie, KU Leuven, Belgium.
Droogmans
G
G
Nilius
B
B
D000255:Adenosine Triphosphate / Q000378:metabolism; D001920:Bradykinin / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D018999:Charybdotoxin / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D005246:Feedback / Q000187:drug effects / Q000502:physiology; D006632:Histamine / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques
D018999:Charybdotoxin; D006632:Histamine; D000255:Adenosine Triphosphate; D001920:Bradykinin; D002118:Calcium