title: Effects of potassium conductance inhibitors on spontaneous diastolic depolarization and abnormal automaticity in human atrial fibers.
abstract: The capability of generating spontaneous diastolic depolarization and automaticity was investigated in vitro by means of standard microelectrode techniques in 50 human atrial preparations. Samples were classified within two groups: group 1 was composed of 12 well-polarized preparations exhibiting action potentials that were fast responses (mean maximum diastolic potential: -75.5 mV and Vmax greater than 100 V/s); group 2 was composed of 38 partially-depolarized samples (mean maximum diastolic potential: -50.3 mV and Vmax less than 10 V/s) and was further divided into two subgroups. Subgroup 2A consisted of 20 spontaneously beating preparations and subgroup 2B consisted of 18 non-automatic partially-depolarized specimens. Highly-polarized fibers from group 1, although exhibiting a slight diastolic depolarization which was almost entirely suppressed by 2 mM caesium, never presented spontaneous activity under our experimental conditions. 90% of automatic fibers from subgroup 2A were sampled from dilated atria. In automatic preparations, diastolic depolarization was usually separated into two phases: an initial phase, also present in non-automatic fibers, and a late phase. Changes in the initial phase were not accompanied by concomitant changes in the spontaneous rate. Abnormal automaticity was clearly related to the late diastolic phase (absent in non-automatic fibers), the generation of which appeared to be a specific property of automatic fibers. The use of K conductance inhibitors (caesium, 4-aminopyridine, barium, low K solutions) provided indirect evidence that neither delayed outward ix current nor if type inward current are principally responsible for abnormal automaticity.
mesh_terms: D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D001145:Arrhythmias, Cardiac / Q000139:chemically induced*; D002586:Cesium / Q000494:pharmacology; D003971:Diastole / Q000187:drug effects*; D004553:Electric Conductivity; D004594:Electrophysiology; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria; D006801:Humans; D009200:Myocardial Contraction / Q000187:drug effects*; D011188:Potassium / Q000037:antagonists & inhibitors* / Q000502:physiology
chemical_list: D000631:Aminopyridines; D002586:Cesium; D015761:4-Aminopyridine; D011188:Potassium