A Na+-activated K+ current (IK,Na) is present in guinea-pig but not rat ventricular myocytes.
The effects of removing extracellular Ca2+ and Mg2+ on the membrane potential, membrane current and intracellular Na+ activity (aiNa) were investigated in guinea-pig and rat ventricular myocytes. Membrane potential was recorded with a patch pipette and whole-cell membrane currents using a single-electrode voltage clamp. Both guinea-pig and rat cells depolarize when the bathing Ca2+ and Mg2+ are removed and the steady-state aiNa increases rapidly from a resting value of 6.4+/- 0.6 mM to 33+/-3.8 mM in guinea-pig (n=9) and from 8.9+/-0.8 mM to 29.3+/-3.0 mM (n=5) in rat ventricular myocytes. Guinea-pig myocytes partially repolarized when, in addition to removal of the bathing Ca2+ and Mg2+, K+ was also removed, however rat cells remained depolarized. A large diltiazem-sensitive inward current was recorded in guinea-pig and rat myocytes, voltage-clamped at -20 mV, when the bathing divalent cations were removed. When the bathing K+ was removed after Ca2+ and Mg2+ depletion, a large outward K+ current developed in guinea-pig, but not in rat myocytes. This current had a reversal potential of -80+/-0.7 mV and was not inhibited by high Mg2+ or glybenclamide indicating that it is not due to activation of non-selective cation or adenosine triphosphate (ATP)-sensitive K channels. The current was not activated when Li+ replaced the bathing Na+ and was blocked by R-56865, suggesting that it was due to the activation of KNa channels.
Lawrence
C
C
Department of Physiology, School of Medical Sciences, University of Otago, Dunedin, New Zealand.
Rodrigo
G C
GC
D000818:Animals; D052160:Benzothiazoles; D002118:Calcium / Q000008:administration & dosage / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D004553:Electric Conductivity; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D008274:Magnesium / Q000008:administration & dosage / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D011188:Potassium / Q000008:administration & dosage / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013844:Thiazoles / Q000494:pharmacology; D016276:Ventricular Function
D052160:Benzothiazoles; D002121:Calcium Channel Blockers; D010880:Piperidines; D015221:Potassium Channels; D013844:Thiazoles; C054551:R 56865; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D004110:Diltiazem; D008274:Magnesium; D011188:Potassium; D005905:Glyburide; D002118:Calcium