Calcium-dependent, slowly inactivating potassium currents in cultured neurons of rat neocortex.
Slowly inactivating outward currents were examined in neurons from rat anterior cortex dissociated at postnatal day 1 and recorded after 7-48 days in vitro by the use of whole-cell patch-clamp technique, in the presence of 0.5-0.8 microM tetrodotoxin (TTX). 50 microM carbachol and 1-5 mM CsCl2. Experiments were often carried out in the additional presence of 1-5 mM CsCl2, which blocks the anomalous, inwardly rectifying IQ, the fast Ca(2+)-dependent K+ current (IC), and 50 microM carbachol, which depresses the IM current. These currents were evoked by depolarizing steps to -40 +/- 5 mV from a conditioning hyperpolarization to -110 +/- 10 mV. Their sensitivity to elevation from 2.5 to 12.5 mM in extracellular K+ concentration, together with their sensitivity to 5-15 mM tetraethylammonium, suggests that they are mainly carried by K+ ions. Their activation and inactivation curves show that the threshold for activation is -65 mV, that their inactivation is achieved at -75 mV and that potentials more negative than -120 mV are needed to abolish it. The time-dependence of de-inactivation gives a maximal current amplitude for conditioning hyperpolarizations of 2 s and is best described by a monoexponential function with a time constant of 0.7 s. Slow transient K+ currents were depressed by low doses of 4-aminopyridine (30-100 microM), which indicates the occurrence of an ID-type component in the recorded K+ currents. No slowly declining K+ current was expressed when a recording solution containing 10 mM 1,2-bis (2-aminophenoxy)ethane-N,N,N'-N'-tetraacetic acid (BAPTA), instead of 1-5 mM BAPTA, was used. When recorded without Ca2+ chelator in the pipette, slowly declining K+ currents were blocked by bath-applied 40-50 microM BAPTA-aminoethoxy, revealing a large-amplitude, rapidly inactivating outward current. This residual component is insensitive to 50 microM 4-aminopyridine and may include a current more related to the IA-type. Our data provide evidence that, in cultured cortical neurons from rat, the expression of an ID-like K+ current is highly dependent on internal Ca2+ concentration.
Hamon
B
B
Laboratoire de Neurobiologie et Neuropharmacologie du Développement, CNRS ERS F0100, Université Paris-sud, Orsay, France.
Audinat
E
E
Gibelin
N
N
Crépel
F
F
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013779:Tetrodotoxin / Q000494:pharmacology
D002614:Chelating Agents; D015221:Potassium Channels; D013779:Tetrodotoxin; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium