Mechanism of fluoride action on the L-type calcium channel in cardiac ventricular myocytes.
The modulatory actions of fluoride on the function of the dihydropyridine-sensitive (L-type) Ca2+ channel were studied in rabbit cardiac myocytes. In cell-attached voltage-clamp experiments, using barium as the charge carrier, fluoride increased the activity of the Ca2+ channel dose-dependently. Low concentrations (<10 mM) of fluoride increased the number of traces with channel activities, and decreased the number of traces without channel activities, resulting in a net increase in the open-channel probability. The effect of 5 mM fluoride on the Ca2+ channel was inhibited by the presence of non-hydrolyzable guanosine diphosphate analog in the cell. On the other hand, high concentrations (>10 mM) of fluoride increased the open-channel duration, resulting in a marked increase in open-channel probability. A pretreatment of myocytes with a phosphatase inhibitor, okadaic acid, virtually abolished the additional effect of fluoride on the open-channel duration or open probability. A concentration of up to 75 mM fluoride had no effect on the Ca2+-channel activity when the myocytes were pretreated with a potent inhibitor of protein kinases, indicating that fluoride increased the Ca2+- channel activity via modulation of the phosphorylation state of the myocyte or the channel protein alone.
Ono
K
K
Department of Physiology, Oita Medical University, Hasama, Japan. ono@oita-med.ac.jp
Arita
M
M
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism*; D002316:Cardiotonic Agents / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011817:Rabbits; D013449:Sulfonamides; D013873:Thionucleotides / Q000378:metabolism / Q000494:pharmacology
D015220:Calcium Channels; D002316:Cardiotonic Agents; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D019319:Okadaic Acid; C023427:guanosine 5'-O-(2-thiodiphosphate); D010749:Phosphoprotein Phosphatases; D019204:GTP-Binding Proteins; D007545:Isoproterenol; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D005459:Fluorides