title: Complexity of the outward K+ current of the rat megakaryocyte.
abstract: Megakaryocytes isolated from rat bone marrow express a voltage-dependent, outward K+ current with complex kinetics of activation and inactivation. We found that this current could be separated into at least two components based on differential responses to K+ channel blockers. One component, which exhibited features of the "transient" or "A-type" K+ current of excitable cells, was more strongly blocked by 4-aminopyridine (4-AP) than by tetrabutylammonium (TBA). This current, which we designated as "4-AP-sensitive" current, activated rapidly at potentials more positive than -40 mV and subsequently underwent rapid voltage-dependent inactivation. A separate current that activated slowly was blocked much more effectively by TBA than by 4-AP. This "TBA-sensitive" component, which resembled a typical delayed rectifier current, was much more resistant to voltage-dependent inactivation. The relative contribution of each of these components varied from cell to cell. The effect of charybdotoxin was similar to that of 4-AP. Our data indicate that the voltage-dependent K+ current of resting megakaryocytes is more complex than heretofore believed and support the emerging concept that megakaryocytes possess intricate electrophysiological properties.
authors.affiliation: Medical Service, Veterans Administration Medical Center, Houston, Texas, USA.
authors.forename: E
authors.initials: E
authors.lastname: Romero
authors.forename: R
authors.initials: R
authors.lastname: Sullivan
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D018999:Charybdotoxin / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D007700:Kinetics; D008533:Megakaryocytes / Q000502:physiology*; D015221:Potassium Channels / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; D018999:Charybdotoxin; D015761:4-Aminopyridine; C009405:tetrabutylammonium