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Adenosine modulation of potassium currents in preganglionic nerve terminals of avian ciliary ganglia
1Department of Physiology University of Sydney, N.S.W., Australia.
Abstract:
Potassium currents in calyciform nerve terminals of the avian ciliary ganglion were analyzed using a single microelectrode voltage clamp. The modulatory affects of adenosine on these currents was also determined. Intracellular CsCl (1 M) blocked the steady-state outward current, indicating that it is mostly carried by K+. Tetraethylammonium (TEA, 10 mM) blocked over 40% of the outward current at a command potential of -30 mV. If Ca2+ influx was blocked by CoCl2 (5 mM), the steady-state outward current was reduced by over 16% in the nerve terminals suggesting that about one fifth of the outward current passes through calcium-activated potassium channels IK(Ca). Adenosine (50 mM) decreased the outward steady-state current over a wide range of command potentials in most terminals studied but failed to decrease this current in the presence of CoCl2 (5 mM). It is concluded that adenosine blocks IK(Ca) in nerve terminals.
Insights
Adenosine inhibits calcium-activated potassium channels (IK(Ca)) in avian ciliary ganglion nerve terminals. This study reveals adenosine
Area of Science:
- Neurophysiology
- Ion Channel Function
Background:
- Avian ciliary ganglion nerve terminals possess complex potassium currents.
- Understanding these currents is crucial for neural signaling.
Purpose of the Study:
- To investigate potassium currents in avian ciliary ganglion nerve terminals.
- To determine the modulatory effects of adenosine on these currents.
Main Methods:
- Single microelectrode voltage clamp technique was employed.
- Pharmacological agents like CsCl, TEA, CoCl2, and adenosine were used to block and modulate currents.
- Analysis of steady-state outward currents was performed.
Main Results:
- Steady-state outward current is primarily carried by potassium (K+).
- Calcium-activated potassium channels (IK(Ca)) contribute approximately one-fifth of the outward current.
- Adenosine significantly decreased the outward steady-state current by blocking IK(Ca).
Conclusions:
- Adenosine specifically blocks calcium-activated potassium channels (IK(Ca)) in avian nerve terminals.
- This action of adenosine suggests a role in modulating neurotransmission at these terminals.