Adenosine potentiates the delayed-rectifier potassium conductance but has no effect on the hyperpolarization-activated Ih current in frog melanotrophs.
The effects of adenosine on the voltage-sensitive delayed-rectifier K+ (IK) currents and hyperpolarization-activated cationic inward current (Ih) were studied in cultured frog melanotrophs using the whole-cell configuration of the patch-clamp technique. The A1 receptor agonist R-N6-phenylisopropyl-adenosine (R-PIA; 50 microM) reversibly increased IK. Perfusion of dibutyryl-cAMP (1 mM) in the external solution did not modify the R-PIA-induced enhancement of IK. Pretreatment of melanotrophs with pertussis toxin (1 microg/ml; 12 h) totally abolished the R-PIA-evoked response. Application of hyperpolarizing voltage pulses from -60 to -120 mV to melanotrophs induced a two-component inward current corresponding to an Ih-like conductance. This conductance was characterized by a high K+ selectivity and a low Na+ permeability and was resistant to tetrodotoxin (1 microM). R-PIA had no effect on Ih. The present study demonstrates that in frog melanotrophs adenosine inhibits the electrical activity by activating IK through an A1 receptor subtype coupled to a pertussis toxin-sensitive pathway independent of the cAMP/PKA system. This study also demonstrates the existence of a Ih conductance in frog melanotrophs which is not modulated by A1 receptors.
Mei
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YA
Dept. of Physiology, Fudan University, Shanghai 200433, China.
Soriani
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Castel
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Vaudry
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H
Cazin
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L
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D054815:Cyclic Nucleotide-Gated Cation Channels; D051668:Delayed Rectifier Potassium Channels; D004357:Drug Synergism; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D058906:Purinergic P1 Receptor Agonists; D011895:Rana ridibunda
D054815:Cyclic Nucleotide-Gated Cation Channels; D051668:Delayed Rectifier Potassium Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D018696:Neuroprotective Agents; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D058906:Purinergic P1 Receptor Agonists; C047235:N-(1-methyl-2-phenylethyl)adenosine; D009074:Melanocyte-Stimulating Hormones; D000241:Adenosine