On the block of outward potassium current in rabbit Schwann cells by internal sodium ions.
Currents through delayed rectifier-type K+ channels in Schwann cells cultured from rabbit sciatic nerve were studied with patch-clamp techniques. When the internal and external solutions contained physiological concentrations of sodium, the amplitude of these outward currents declined as the cell was depolarized to potentials above about +40 mV, despite the increased driving force. This reduction in the amplitude of outward K+ currents was observed in many cells before the subtraction of leakage currents; it was also observed for ensemble currents recorded in outside-out patches. It was therefore not the result of a leak-subtraction artefact nor of inadequate voltage-clamp control. Several lines of evidence also suggested that it was not the result of the extracellular accumulation of K+. By contrast, when the Na+ ion concentration of the internal solution was nominally zero, the reduction in the amplitude of outward K+ currents at positive membrane potentials was not observed. The apparent amplitude of single-channel currents through two types of K+ channel was reduced by 30 mM internal Na+, apparently as the result of a rapid 'flickery' block. The results suggest that channel block by internal Na+ is largely responsible for the negative slope conductance seen in current-voltage plots of whole-cell K+ currents at positive membrane potentials. In addition, our analysis of single-channel currents suggests that the current-voltage curve for a delayed rectifier channel in rabbit Schwann cells (in the absence of internal Na+) is roughly linear with internal and external K+ concentrations of 140 mM and 5.6 mM, respectively.
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
J R
JR
Howe
M
M
Baker
J M
JM
Ritchie
D000818:Animals; D004594:Electrophysiology; D005071:Evoked Potentials; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D017136:Ion Transport; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D011817:Rabbits; D012583:Schwann Cells / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D015221:Potassium Channels; D012964:Sodium; D011188:Potassium