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Delayed rectifier current of bullfrog sympathetic neurons: ion‐ion competition, asymmetrical block and effects of ions on gating.
Author(s) -
Block B M,
Jones S W
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1997.sp021937
Subject(s) - chemistry , bullfrog , tetraethylammonium , extracellular , biophysics , patch clamp , gating , ion , ion channel , reversal potential , analytical chemistry (journal) , potassium , biochemistry , chromatography , medicine , receptor , organic chemistry , biology
1. The delayed rectifier (DR) K+ channel pore was probed using different permeant and blocking ions applied intra‐ and extracellularly. Currents were recorded from bullfrog sympathetic neurons using whole‐cell patch‐clamp techniques. 2. With intra‐ and extracellular Cs+ (0 K+), there were large, tetraethylammonium (TEA)‐sensitive currents. Adding K+ back to the extracellular solution revealed that the current with Cs+i was K+ selective (permeability ratio PCs/PK = 0.17 +/‐ 0.02, n = 4) and showed a strong anomalous mole fraction effect. 3. There were also large non‐inactivating currents with Na+i and Na+o (0 K+). The current with Na+i was K+ selective (Na+o vs. K+o: PNa/PK = 0.022 +/‐ 0.005, n = 5), and was TEA sensitive with K+o but not with Na+o. 4. Permeant ions affected gating kinetics. DR currents activated faster in K+ than in Cs+, and activated faster with increasing concentrations of either K+ or Cs+. Deactivation was slowed by increased K+ or Cs+ concentration, with no difference between K+ and Cs+. 5. The pore was also characterized using intracellular blocking ions. A wide variety of monovalent cations (TEA, N‐methyl‐D‐glucamine, arginine, choline, CH3NH3+, Li+, Cs+ and Na+) blocked DR channels from the inside in a voltage‐dependent manner: KD at 0 mV was 2.9 mM for TEA and 134‐487 mM for the others, at apparent electrical distances (delta) of 0.33‐0.79. There was no detectable block by 10 mM Mgi2+. Apart from TEA, the organic cations did not block from the outside. 6. The permeability to Na+ in the absence of K+, and the strong anomalous mole fraction effects observed for Cs+o + K+o mixtures, suggest that DR channels select for K+ using ion‐ion competition. The block by large intracellular cations shows that the pore is asymmetrical. The loss of high affinity TEAo block with Na+i and Na+o, and the effects of permeant ions on gating, suggest that channel conformation may be affected by ions in the pore.