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Voltage-dependent potassium channels in activated rat microglia.
J Physiol. 1994 Feb 15; 475(1):15-32.JP

Abstract

1. Voltage-dependent currents of untreated (proliferating) and lipopolysaccharide (LPS)-treated rat microglial cells in culture were recorded using the whole-cell patch-clamp technique. 2. Membrane potentials showed prominent peaks at -35 mV and -70 mV. Membrane potentials of LPS-treated cells alternated between the two values. This may be due to a negative slope region of the I-V relation resulting in two zero current potentials. 3. From a holding potential of -70 mV, hyperpolarizing steps evoked an inwardly rectifying current both in proliferating and in LPS-treated cells, while depolarizing steps below -50 mV evoked an outwardly rectifying current only in LPS-treated microglia. The currents were K+ selective, as indicated by their reversal potential of approximately 0 mV in symmetric K+ concentrations (150 mM both intra- and extracellularly) and the reversal potential of the outward tail currents of approximately -90 mV at a normal extracellular K+ concentration (4.5 mM). 4. The activation of the outward current could be fitted by Hodgkin-Huxley-type n4 kinetics. The time constant of activation depended on voltage. 5. The inactivation of the inward and outward currents could be fitted by a single exponential. The time constant of the inward current inactivation was dependent on voltage, whereas the time constant of the outward current inactivation was virtually independent of voltage, except near the threshold of activation. Recovery of the outward from inactivation was slow and could be fitted by two exponentials. Responses to depolarizing steps were stable at 0.125 Hz, but greatly decreased from the first to the second pulse at 1 Hz. 6. The inactivation of the inward, but not of the outward, current disappeared in a low Na(+)-containing medium (5 mM). The inward current was selectively inhibited by extracellular Cs+ and Ba2+. The outward current was selectively inhibited by Cd2+, 4-aminopyridine and charybdotoxin. Replacement of intracellular K+ by an equimolar concentration of Cs+, and the extracellular application of tetraethylammonium and quinine inhibited both currents. 7. An increase of extracellular Ca2+ from 2 to 20 mM resulted in outwardly rectifying K+ channels activating at more positive potentials. Omission of Ca2+ from the extracellular medium had the opposite effect. When the intracellular free Ca2+ was increased from 0.01 to 1 microM, the outward current amplitudes were depressed. The Ca2+ ionophore A23187 had a similar effect. 8. LPS-treated microglial cells possess inwardly and outwardly rectifying K+ channels. The physiological and pharmacological characteristics of these two channel populations are markedly different.(

ABSTRACT

TRUNCATED AT 400 WORDS)

Authors+Show Affiliations

Department of Pharmacology, University of Freiburg, FRG.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

7514664

Citation

Nörenberg, W, et al. "Voltage-dependent Potassium Channels in Activated Rat Microglia." The Journal of Physiology, vol. 475, no. 1, 1994, pp. 15-32.
Nörenberg W, Gebicke-Haerter PJ, Illes P. Voltage-dependent potassium channels in activated rat microglia. J Physiol. 1994;475(1):15-32.
Nörenberg, W., Gebicke-Haerter, P. J., & Illes, P. (1994). Voltage-dependent potassium channels in activated rat microglia. The Journal of Physiology, 475(1), 15-32.
Nörenberg W, Gebicke-Haerter PJ, Illes P. Voltage-dependent Potassium Channels in Activated Rat Microglia. J Physiol. 1994 Feb 15;475(1):15-32. PubMed PMID: 7514664.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Voltage-dependent potassium channels in activated rat microglia. AU - Nörenberg,W, AU - Gebicke-Haerter,P J, AU - Illes,P, PY - 1994/2/15/pubmed PY - 1994/2/15/medline PY - 1994/2/15/entrez SP - 15 EP - 32 JF - The Journal of physiology JO - J Physiol VL - 475 IS - 1 N2 - 1. Voltage-dependent currents of untreated (proliferating) and lipopolysaccharide (LPS)-treated rat microglial cells in culture were recorded using the whole-cell patch-clamp technique. 2. Membrane potentials showed prominent peaks at -35 mV and -70 mV. Membrane potentials of LPS-treated cells alternated between the two values. This may be due to a negative slope region of the I-V relation resulting in two zero current potentials. 3. From a holding potential of -70 mV, hyperpolarizing steps evoked an inwardly rectifying current both in proliferating and in LPS-treated cells, while depolarizing steps below -50 mV evoked an outwardly rectifying current only in LPS-treated microglia. The currents were K+ selective, as indicated by their reversal potential of approximately 0 mV in symmetric K+ concentrations (150 mM both intra- and extracellularly) and the reversal potential of the outward tail currents of approximately -90 mV at a normal extracellular K+ concentration (4.5 mM). 4. The activation of the outward current could be fitted by Hodgkin-Huxley-type n4 kinetics. The time constant of activation depended on voltage. 5. The inactivation of the inward and outward currents could be fitted by a single exponential. The time constant of the inward current inactivation was dependent on voltage, whereas the time constant of the outward current inactivation was virtually independent of voltage, except near the threshold of activation. Recovery of the outward from inactivation was slow and could be fitted by two exponentials. Responses to depolarizing steps were stable at 0.125 Hz, but greatly decreased from the first to the second pulse at 1 Hz. 6. The inactivation of the inward, but not of the outward, current disappeared in a low Na(+)-containing medium (5 mM). The inward current was selectively inhibited by extracellular Cs+ and Ba2+. The outward current was selectively inhibited by Cd2+, 4-aminopyridine and charybdotoxin. Replacement of intracellular K+ by an equimolar concentration of Cs+, and the extracellular application of tetraethylammonium and quinine inhibited both currents. 7. An increase of extracellular Ca2+ from 2 to 20 mM resulted in outwardly rectifying K+ channels activating at more positive potentials. Omission of Ca2+ from the extracellular medium had the opposite effect. When the intracellular free Ca2+ was increased from 0.01 to 1 microM, the outward current amplitudes were depressed. The Ca2+ ionophore A23187 had a similar effect. 8. LPS-treated microglial cells possess inwardly and outwardly rectifying K+ channels. The physiological and pharmacological characteristics of these two channel populations are markedly different.(ABSTRACT TRUNCATED AT 400 WORDS) SN - 0022-3751 UR - https://www.unboundmedicine.com/medline/citation/7514664/Voltage_dependent_potassium_channels_in_activated_rat_microglia_ L2 - https://onlinelibrary.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0022-3751&date=1994&volume=475&spage=15 DB - PRIME DP - Unbound Medicine ER -