Hypoxia increases persistent sodium current in rat ventricular myocytes.
1. A persistent inward current activated by depolarization was recorded using the whole-cell, tight seal technique in rat isolated cardiac myocytes. The amplitude of the inward current increased when cells were exposed to a solution with low oxygen tension. 2. The persistent inward current had the characteristics of the persistent Na+ current described previously in rat ventricular myocytes: it was activated at negative potentials (-70 mV), reversed close to the equilibrium potential for Na+ (ENa), was blocked by TTX and was resistant to inactivation. 3. Persistent single Na+ channel currents activated by long (200-400 ms) depolarizations were recorded in cell-attached patches on isolated ventricular myocytes. Hypoxia increased the frequency of opening of the persistent Na+ channels. 4. Persistent Na+ channels recorded during hypoxia had characteristics similar to those of persistent Na+ channels recorded at normal oxygen tensions. They had a null potential at ENa, their amplitude varied with [Na+], they were resistant to inactivation and their mean open time increased with increasing depolarization. 5. The persistent Na+ channels in cell-attached patches were blocked by TTX (50 microM) in the patch pipette and by lidocaine (100 microM). 6. It was concluded that hypoxia increases the open probability of TTX-sensitive, inactivation-resistant Na+ channels. The voltage dependence of these channels, and their greatly increased activity during hypoxia, suggest that they may play an important role in the generation of arrhythmias during hypoxia.
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John Curtin School of Medical Research, Australian National University, Canberra, Australia.
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Gage
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D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D004594:Electrophysiology; D006352:Heart Ventricles / Q000737:chemistry / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008012:Lidocaine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D015222:Sodium Channels / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D000889:Anti-Arrhythmia Agents; D015222:Sodium Channels; D013779:Tetrodotoxin; D008012:Lidocaine; D012964:Sodium