Voltage-gated sodium and calcium currents in rat osteoblasts.
1. The whole-cell voltage-clamp mode of the patch-clamp technique was used to investigate the presence of voltage-gated inward currents in osteoblasts from newborn rat calvaria. 2. In K+-free solutions, three kinds of inward currents could be activated by depolarization: a voltage-gated Na+ current and two different types of Ca2+ currents. 3. The Na+ current was activated by depolarization above -40 mV in all the cells. It was reduced by half by 10 nM-TTX (tetrodotoxin). 4. In an isotonic Ba2+ external solution containing TTX, and with a Cs-EGTA internal solution buffered at pCa 8, depolarizing jumps induced both a transient Ba2+ current and a sustained Ba2+ current. The relative proportions of these two currents varied greatly among cells. 5. The transient and sustained Ba2+ currents differ with respect to their time course and their voltage dependence. 6. The depolarization-activated inward currents were also observed under more physiological conditions, in the presence of only 2 mM-external Ca2+ and with a K+ internal solution buffered at pCa 7. 7. A few records obtained in current clamp showed that it is possible to induce action potentials in osteoblasts.
Chesnoy-Marchais
D
D
Laboratoire de Neurobiologie, Ecole Normale Supérieure, Paris, France.
Fritsch
J
J
D000818:Animals; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D008564:Membrane Potentials / Q000187:drug effects; D010006:Osteoblasts / Q000502:physiology*; D010010:Osteoclasts / Q000187:drug effects; D051381:Rats; D012964:Sodium / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D001464:Barium; D013779:Tetrodotoxin; D012964:Sodium; D002118:Calcium