Sodium current in single rat heart muscle cells.
1. Rapid inward Na current (INa) was studied in isolated cells from rat ventricular myocardium by a double-suction-pipette voltage clamp technique. All experiments were carried out at 20-22 degrees C. 2. INa elicited by single depolarizing voltage steps from a holding potential, VH, of -80 mV had a threshold between -70 and -60 mV and was maximal at -30 to -20 mV. Peak currents in Krebs-Ringer solution containing 145 mM Na were of the order 0.9-1.8 mA cm-2, assuming an average cell surface area of 8000 square micrometers. 3. The reversal potential for INa was predicted by the Nernst equation for external Na in the range 1.45-145 mM with 16 mM-Na solution perfusing the interior of the cell. 4. Instantaneous I-V plots were linear for potentials of -100 to + 10 mV. Maximum Na conductance (-gNa) was calculated to be 25 mS cm-2 in 145 mM-Na solutions and gNa was constant for potentials positive to -10 mV. 5. INa activated with a time constant of 0.7 msec at -55 mV, decreasing to 100 microsec on depolarizations positive to + 10 mV. 6. Two time constants (tau h1, tau h2) were required to describe INa inactivation during a maintained depolarization, with tau h2 three to four times as long as tau h1. tau h1 was about 2 msec at -50 mV, decreasing to 0.9 msec at -10 mV. 7. The time course for recovery of INa from inactivation also exhibited two time constants (tau r1, tau r2), with the longer tau r2 having a maximum value of the order 100 msec in the potential range -60 to -80 mV. 8. INa in isolated rat cardiac cells has a low sensitivity to tetrodotoxin, requiring a concentration of 30 micrometers for complete blockade.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000166:cytology*; D051381:Rats; D012964:Sodium / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D016276:Ventricular Function
D013779:Tetrodotoxin; D012964:Sodium