title: Number of K(Ca) channels underlying spontaneous miniature outward currents (SMOCs) in mudpuppy cardiac neurons.
abstract: Spontaneous miniature outward currents (SMOCs) in parasympathetic neurons from mudpuppy cardiac ganglia are caused by activation of TEA- and iberiotoxin-sensitive, Ca(2+)-dependent K(+) (BK) channels. Previously we reported that SMOCs are activated by Ca(2+)-induced Ca(2+) release (CICR) from caffeine- and ryanodine-sensitive intracellular Ca(2+) stores. In the present study, we analyzed the single channel currents that contribute to SMOC generation in mudpuppy cardiac neurons. The slope conductance of BK channels, determined from the I-V relationship of single-channel currents recorded with cell-attached patches in physiological K(+) concentrations, was 84 pS. The evidence supporting the identity of this channel as the channel involved in SMOC generation was its sensitivity to internal Ca(2+), external TEA, and caffeine. In cell-attached patch recordings, 166 microM TEA applied in the pipette reduced single-channel current amplitude by 32%, and bath-applied caffeine increased BK channel activity. The ratio between the averaged SMOC amplitude and the single-channel current amplitude was used to estimate the average number of channels involved in SMOC generation. The estimated number of channels involved in generation of an averaged SMOC ranged from 18 to 23 channels. We also determined that the Po of the BK channels at the peak of a SMOC remains constant at voltages more positive than -20 mV, suggesting that the transient rise in intracellular Ca(2+) from ryanodine-sensitive intracellular stores in the vicinity of the BK channel reached concentrations most likely exceeding 40 microM.
authors.affiliation: Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, Vermont 05405, USA.
authors.forename: F S
authors.initials: FS
authors.lastname: Scornik
authors.forename: L A
authors.initials: LA
authors.lastname: Merriam
authors.forename: R L
authors.initials: RL
authors.lastname: Parsons
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009338:Necturus maculosus; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D019789:Tetraethylammonium / Q000494:pharmacology
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D002110:Caffeine; D019789:Tetraethylammonium; D011188:Potassium; D002118:Calcium