Two Kinds of Transient Outward Currents, I
A
and I
Adepol
, in F76 and D1 Soma Membranes of the Subesophageal Ganglia of Helix aspersa |
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Authors: | R Bal M Janahmadi GGR Green DJ Sanders |
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Institution: | (1) Department of Physiology, University Medical School, Newcastle Upon Tyne, NE2 4HH, UK, GB |
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Abstract: | Transient outward currents were characterized with twin electrode voltage clamp techniques in isolated F76 and D1 neuronal
membranes (soma only) of Helix aspersa subesophageal ganglia. In this study, in addition to the transient outward current (A-current, I
A
) described by Connor and Stevens (1971b), another fast outward current, referred to as I
Adepol
here, is described for the first time. This is similar to the current component characterized in Aplysia (Furukawa, Kandel & Pfaffinger, 1992). The separation of these two current components was based on activation and steady-state
inactivation curves, holding potentials and sensitivity to 4-aminopyridine (4-AP). In contrast to I
A
, I
Adepol
did not require hyperpolarizing conditioning pulses to remove inactivation; it was evoked from a holding potential of −40
mV, at which I
A
is completely inactivated. I
Adepol
shows noticeable activation at around −5 mV, whereas I
A
activates at around −50 mV. The time courses of I
Adepol
activation and inactivation were similar but slower than I
A
. It was found that I
Adepol
was more sensitive than I
A
to 4-AP. 4-AP at a concentration of 1 mm blocked I
Adepol
completely, whereas 5–6 mm 4-AP was needed to block I
A
completely. This current is potentially very important because it may, like other A currents, regulate firing frequency but
notably, it does not require a period of hyperpolarization to be active.
Received: 12 May 2000/Revised: 12 October 2000 |
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Keywords: | : Transient outward currents — A-current — Potassium current — Soma membranes — Electrophysiology — In vitro |
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