Nitric oxide modulation of calcium-activated potassium channels in postganglionic neurones of avian cultured ciliary ganglia.
1. A study has been made of the modulation of calcium-activated potassium channels in cultured neurones of avian ciliary ganglia by sodium nitroprusside and L-arginine. 2. Sodium nitroprusside (100 microM) reduced the net outward current by 22 +/- 1% at 4.8 ms (mean +/- s.e. mean) and 25 +/- 1% at 350 ms during a test depolarization to +40 mV from a holding potential of -40 mV. The outward current remained reduced for the duration of the recording following a single application of sodium nitroprusside. These effects did not occur if the influx of calcium ions was first blocked with Cd2+ (500 microM). Application of ferrocyanide (100 microM) reduced the net outward current by only 6 +/- 3% at 350 ms during a test depolarization to +40 mV. 3. L-Arginine (270 microM) reduced the net outward current on average by 19 +/- 2% at 4.8 ms and 22 +/- 2% at 350 ms during a test depolarization to +40 mV. The current remained in this reduced state for the duration of the recording following a single application of L-arginine. These effects were reduced to 11 +/- 1% at 4.8 ms and 11 +/- 2% at 350 ms in the presence of N omega-nitro-L-arginine methyl ester (L-NAME, 100 microM). 4. In order to alleviate the dependence of calcium-activated potassium channels (Ik(Ca)) on the inward flux of calcium ions, the patch-clamp pipettes were filled with a solution containing 100 microM CaCl2, and the Ca2+ in the bathing solution was replaced with EGTA. Under these conditions sodium nitroprusside reduced the total outward current during a depolarizing pulse of + 40 mV by 9 +/_ 1% at 4.8 ms and by 36 +/- 3% at 350 ms. L-Arginine (270 microM) reduced this current under the same conditions by 9 +/- 1% at 4.8 ms and by 35 +/- 2% at 350 ms.5. Calcium-activated potassium currents were sensitive to apamin (50 nM), as this reduced the outward current by 23 +/- 3% at 350 ms when a high calcium-containing pipette was used during a depolarizing command to + 40 mV. L-Arginine still decreased the outward current in the presence of apamin(50 nM), by 5 +/- 1% at 4.8 ms and by 19 +/- 2% at 350 ms, indicating that L-arginine could reduce an apamin-insensitive Ik(Ca)6. Calcium-activated potassium currents were also sensitive to charybdotoxin (10 nM), as this reduced the outward current by 34 +/- 4% at 350 ms when a high calcium-containing pipette was used during a depolarizing command to + 40 mV. L-Arginine still decreased the outward current in the presence of charybdotoxin, by 6 +/- 1% at 4.8 ms and 12 +/- 4% at 350 ms, showing that L-arginine could reduce a charybdotoxin-insensitive Ik(Ca).7. The present results indicate that NO-synthase in ciliary ganglia can modulate Ik(Ca) by a method which is independent of the action of NO on the calcium channels. The Ik(ca) is decreased significantly at 4.8 ms into a depolarizing pulse, at a time that would decrease the rate of repolarization of the action potential. Ik(Ca) is also reduced at longer times (350 ms), indicating an affect on the inactivating process.
Cetiner
M
M
Department of Physiology, University of Sydney, N.S.W., Australia.
Bennett
M R
MR
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D001338:Autonomic Fibers, Postganglionic / Q000187:drug effects* / Q000502:physiology*; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002642:Chick Embryo; D002923:Cilia / Q000187:drug effects / Q000502:physiology; D046508:Culture Techniques; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D017774:Long-Term Potentiation / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology* / Q000502:physiology; D009599:Nitroprusside / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology*
D018377:Neurotransmitter Agents; D015221:Potassium Channels; D002104:Cadmium; D009599:Nitroprusside; D009569:Nitric Oxide; D001120:Arginine; D002118:Calcium