ISSN:
1432-1106
Keywords:
Slowly inactivating potassium currents
;
Patch-clamp
;
Cortical neurons
;
Rat
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract 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 μM tetrodotoxin (TTX), 50 μM 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 I Q, the fast Ca 2 + -dependent K+ current (I C), and 50 μM carbachol, which depresses the I M 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 μM), which indicates the occurrence of an I D-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 μM BAPTA-aminoethoxy, revealing a large-amplitude, rapidly inactivating outward current. This residual component is insensitive to 50 μM 4-aminopyridine and may include a current more related to the I A-type. Our data provide evidence that, in cultured cortical neurons from rat, the expression of an I D-like K+ current is highly dependent on internal Ca2+ concentration.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00230041
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