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The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.
Author(s) -
Plant T D
Publication year - 1986
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.1986.sp016107
Subject(s) - conductance , rubidium , ion , chemistry , potassium , depolarization , atomic physics , tetraethylammonium , biophysics , analytical chemistry (journal) , physics , condensed matter physics , biology , organic chemistry , chromatography
The effects of replacement of external and internal K+ ions by Rb+ ions on the two fast components (gf1 and gf2) and slow component (gs) of the K+ conductance (gK) in frog nodes of Ranvier were investigated under voltage‐ and current‐clamp conditions. Fast and slow components of gK were separated by double exponential fits to tail currents following long depolarizing pre‐pulses, or by the use of short pre‐pulses which activate little gs X gs was also isolated by 1 mM‐4‐aminopyridine (4‐AP). gf1 and gf2 were distinguished in the fast conductance‐voltage curve by their different voltage dependences, gf1 activating at more negative potentials. Reversal potential measurements indicated that Rb+ is less permeant than K+, and measurements in 4‐AP indicated that the slow component has a lower Rb+ permeability than the fast. In a 50% K+, 50% Rb+ mixture PRb/PK was less than that in 100% Rb+ suggesting that PRb/PK is mole‐fraction dependent. With external Rb+ the current‐voltage relation was shifted by ca.‐10 mV compared to that in K+, an effect on gf ( = gf1 + gf2). The slow conductance (gs) and, under similar conditions, the Na+ current‐voltage relation were not shifted. gf, calculated from inward tail currents, was reduced with external Rb+ at potentials where gf2 was activated. Instantaneous current‐voltage relations following pre‐pulses which activate different components of gf confirmed these observations. In K+ the instantaneous current‐voltage relation showed some inward rectification which was largely abolished with Rb+. Comparison of gf calculated from outward (go) and inward (gi) currents confirmed this, and showed that inward gf2 was reduced with Rb+ such that go = gi. Outward currents were little affected by external Rb+. External Rb+ slowed the fast inward tail current following all pre‐pulses which activate gf, but had no effect on the time course of the slow component of the tail current. Regenerative responses, which occur in high [K+] (+300 nM‐tetrodotoxin) solutions in current clamp did not repolarize in Rb+. Voltage‐clamp experiments showed that inactivation of inward currents is slowed when Rb+ is the charge carrier. Replacement of internal K+, by application of Rb+ to the cut ends of the fibre, shifted the reversal potential to more positive potentials but had no effect on the conductance or kinetics. External Rb+ has a large number of effects on inward currents, but little effect on outward currents. Internal Rb+ had little effect on outward or inward currents.(ABSTRACT TRUNCATED AT 400 WORDS)