Contrasting effects of intracellular redox couples on the regulation of maxi-K channels in isolated myocytes from rabbit pulmonary artery.
1. The effects of intracellular redox couples were investigated on the activation by voltage, Ca2+ and NS 1619 of maxi-K channels in enzymatically isolated smooth muscle cells from large pulmonary arteries of rabbits. 2. In inside-out membrane patches, maxi-K channels were characterized by a single-channel conductance of 266 pS in symmetrical 140 mM KCl solutions. The relationship between the open-state probability (Po) and the membrane potential could be fitted to the Boltzmann equation. The activating action of intracellular Ca2+ was reversible, concentration dependent, and was manifested as the reduction in the voltage necessary to half-activate the channel (V1/2) with no change in the slope factor. NS 1619 also predisposed the maxi-K channel to open at more hyperpolarized membrane potentials. 3. The oxidizing agent 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB, 1 mM) activated maxi-K channels by inducing a negative shift of the activity-voltage curve, while the reducing agent 2-hydroxy-1-ethanethiol (beta-mercaptoethanol) (BME, 1 mM) had no effect. DTNB increased the efficacy of Ca2+ in activating maxi-K channels. The action of DTNB was not reversible upon wash-out, but could be counteracted by BME. 4. Maxi-K channel activity was unaffected by other oxidizing agents, such as NAD (2 mM) and glutathione disulphide (GSSG, 5 mM), or by their reduced forms (NADH and GSH). Mg-ATP (0.1 and 1 mM) increased the channel activity in a dose-dependent manner, while guanine nucleotides (100 microM GTP gamma S, 500 microM GDP and 200 microM GDP beta S) had no effect. 5. Our data suggest that a change in the intracellular redox state, which would be expected during acute hypoxia, does not alter the activity of maxi-K channels of large pulmonary artery smooth muscle cells. The sulfhydryl-specific redox reagents (DTNB and BME) must act through another regulatory mechanism.
Thuringer
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CNRS UMR 6542, Faculté des Sciences et Techniques, Université de Tours, France. thuringer@balzac.univ.tours.fr
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D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004594:Electrophysiology; D005978:Glutathione / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011651:Pulmonary Artery / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D013439:Sulfhydryl Reagents
D001562:Benzimidazoles; D015221:Potassium Channels; D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D009243:NAD; C086491:NS 1619; D011189:Potassium Chloride; D004228:Dithionitrobenzoic Acid; D005978:Glutathione; D002118:Calcium