title: Role of a pertussis toxin-sensitive protein in the modulation of canine Purkinje fiber automaticity.
abstract: We previously have shown that alpha-adrenergic stimulation of canine Purkinje fibers and rat ventricle decreases automaticity. Experiments on rat ventricular myocytes in tissue culture have suggested that the decrease in automaticity induced by alpha-adrenergic stimulation depends on the development of sympathetic innervation and the presence of a pertussis toxin-sensitive, 41-kDa guanosine triphosphate (GTP)-regulatory protein. In the present study, microelectrode and biochemical techniques were used to test the role of the pertussis toxin-sensitive protein and sympathetic innervation in modulating automaticity of adult canine Purkinje fibers. Fibers were incubated in Tyrode's solution alone or in Tyrode's solution plus pertussis toxin (0.1-0.5 microgram/ml) for 24 hours and were then superfused with phenylephrine. Phenylephrine in the 5 x 10(-9)-5 x 10(-8) M range induced a decrease in automaticity in 63% of the 16 fibers not treated with pertussis toxin and an increase in automaticity in 37%. The former group had a higher level of pertussis toxin-sensitive substrate by the [32P]nicotinamide adenine dinucleotide adenosine diphosphate (ADP)-ribosylation assay than the latter. In contrast, all fibers treated with pertussis toxin (0.5 microgram/ml) showed increased automaticity in response to phenylephrine and had no detectable pertussis toxin-sensitive substrate. Over the range of pertussis toxin concentrations studied, there was a smooth concentration-response relation between the substrate levels measured and the automatic response to phenylephrine. As ADP-ribosylatable substrate levels decreased, the percent of fibers showing an increase in automaticity increased.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D006329:Heart Conduction System / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D016627:Oxidopamine; D037342:Pertussis Toxin; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects* / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D006892:Hydroxydopamines; D010566:Virulence Factors, Bordetella; D010656:Phenylephrine; D000246:Adenosine Diphosphate Ribose; D016627:Oxidopamine; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D011224:Prazosin