Permeability characteristics of monovalent cations in atrial myocytes of the rat heart.
We investigated the permeability of Cs+ and Na+ through various ion channels in rat atrial myocytes using the whole-cell voltage-clamp technique. With isotonic CsCl (140 mM) on both sides of the membrane and nominally [Ca2+]o-free conditions, depolarising clamp pulses induced an increase of outward currents which showed a biphasic time course. Repolarisation to the holding potential induced inward tail currents. With isotonic NaCl, depolarisation also induced outward currents which showed a monotonic decay, but inward tail currents were not observed. Both in NaCl and CsCl, currents were hardly affected by TEA (10 mM), 4-AP (5 mM) and DIDS (100 microM). Nicardipine (1 M) almost completely blocked time-dependent outward currents in isotonic NaCl solution, leaving only time-independent currents which showed linear I-V relationship. In isotonic CsCl conditions, nicardipine blocked outward current considerably, but there still remained time-dependent outward currents and inward tail currents. Addition of E-4031 (2-20 M) which is known as a specific blocker of the rapidly activating delayed rectifier K+ current (IKr) completely blocked these time-dependent outward and inward currents, leaving only a time-independent current. Time-independent currents recorded in the presence of nicardipine and E-4031 were inhibited by GdCl3, which is known to block non-selective cation (NSC) currents. From these results, it was suggested that NSC current in atrial myocytes can be investigated in isotonic Cs+ or Na+ solution in the presence of Ca2+ channel and IKr blockers.
Youm
J B
JB
Department of Physiology and Heart Research Institute, Seoul National University College of Medicine, 28 Yonkeun-Dong, Chongno-Ku, Seoul 110-799, Korea.
Ho
W K
WK
Earm
Y E
YE
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D027682:Cation Transport Proteins; D002414:Cations, Monovalent / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D004553:Electric Conductivity; D051638:Ether-A-Go-Go Potassium Channels; D005682:Gadolinium / Q000494:pharmacology; D006325:Heart Atria; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009529:Nicardipine / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D002121:Calcium Channel Blockers; D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D051638:Ether-A-Go-Go Potassium Channels; C092509:KCNH6 protein, human; D010880:Piperidines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011725:Pyridines; C063968:E 4031; D005682:Gadolinium; D009529:Nicardipine