The electrical activity of canine cardiac Purkinje fibers in sodium-free, calcium-rich solutions.
Propagated action potentials can be obtained in canine cardiac Purkinje fibers exposed to Na-free solutions containing no inorganic cation other than Ca and K. Essentially similar action potentials are obtained if Na is replaced by tetraethylammonium (TEA), tetramethylammonium (TMA), or choline. In a solution containing 128 mM TEA and 16.2 mM Ca the characteristics of these electrical responses were: maximum diastolic potential, -59 +/- 3.3 mV; overshoot, 20 +/- 6.8 mV; maximum upstroke velocity, 3.7 +/- 2.3 V/s; conduction velocity, 0.1 m/s; and action potential duration, 360 +/- 45 ms. The magnitude of the overshoot varied with log Ca(o) with a slope of about 30 mV/10-fold concentration change. The upstroke velocity was an approximately linear function of Ca(o). The active response was greatly diminished or abolished by Mn and D-600 but was unaffected by tetrodotoxin. These Ca-dependent responses appeared in a region of transmembrane potential (about -50 mV) at which the rapid Na-dependent upstroke is abolished even when Na is present.
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002794:Choline / Q000494:pharmacology; D004285:Dogs; D004558:Electric Stimulation; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012964:Sodium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D000644:Quaternary Ammonium Compounds; D013757:Tetraethylammonium Compounds; D013779:Tetrodotoxin; D012964:Sodium; D008274:Magnesium; D002794:Choline; D002118:Calcium