Open sodium channel properties of single canine cardiac Purkinje cells.
Open channel properties of canine cardiac Purkinje cell Na+ channels were studied with single channel cell-attached recording and with whole cell macroscopic current recording in internally perfused cells. Single channel currents and membrane currents increased with an increase in Na+ concentration, but showed evidence of saturation. Assuming first-order binding, the Km for Na+ was 370 mM. PCs/PNa was 0.020 and PK/PNa was 0.094. The current-voltage relationship for single channels showed prominent flattening in the hyperpolarizing direction. This flattening was accentuated by 10 mM Ca2+ and was greatly reduced in O mM Ca2+, indicating that the rectification was a consequence of Ca2+ block of the Na+ channels. A similar instantaneous current-voltage relationship was seen for the whole cell membrane currents. These results demonstrate that the cardiac channel shows substantial Ca2+ block, although it is relatively insensitive to tetrodotoxin. The Na+ and Ca2+ binding properties could be modeled by the four-barrier Eyring rate theory model, with similar values to those reported for the neuroblastoma Na+ channel (Yamamoto, D.,J.Z. Yeh, and T. Narahashi, 1984, Biophys J., 45:337-344).
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004285:Dogs; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D010477:Perfusion; D011690:Purkinje Fibers / Q000502:physiology*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D007473:Ion Channels; D013779:Tetrodotoxin; D012964:Sodium; D002118:Calcium