title: Outward currents in smooth muscle cells isolated from sheep mesenteric lymphatics.
abstract: 1. The patch-clamp technique was used to measure membrane currents in isolated smooth muscle cells dispersed from sheep mesenteric lymphatics. Depolarizing steps positive to -30 mV evoked rapid inward currents followed by noisy outward currents. 2. Nifedipine (1 microM) markedly reduced the outward current, while Bay K 8644 (1 microM) enhanced it. Up to 90% of the outward current was also blocked by iberiotoxin (Kd = 36 nM). 3. Large conductance (304 +/- 15 pS, 7 cells), Ca(2+)- and voltage-sensitive channels were observed during single-channel recordings on inside-out patches using symmetrical 140 mM K+ solutions (at 37 degrees C). The voltage required for half-maximal activation of the channels (V1/2) shifted in the hyperpolarizing direction by 146 mV per 10-fold increase in [Ca2+]i. 4. In whole-cell experiments a voltage-dependent outward current remained when the Ca(2+)-activated current was blocked with penitrem A (100 nM). This current activated at potentials positive to -20 mV and demonstrated the phenomenon of voltage-dependent inactivation (V1/2 = -41 +/- 2 mV, slope factor = 18 +/- 2 mV, 5 cells). 6. Tetraethylammonium (TEA; 30 mM) reduced the voltage-dependent current by 75% (Kd = 3.3 mM, 5 cells) while a maximal concentration of 4-aminopyridine (4-AP; 10 mM) blocked only 40% of the current. TEA alone had as much effect as TEA and 4-AP together, suggesting that there are at least two components to the voltage-sensitive K+ current. 7. These results suggest that lymphatic smooth muscle cells generate a Ca(2+)-activated current, largely mediated by large conductance Ca(2+)-activated K+ channels, and several components of voltage-dependent outward current which resemble 'delayed rectifier' currents in other smooth muscle preparations.
authors.affiliation: Department of Physiology, School of Biomedical Science, Queen's University of Belfast, UK.
authors.forename: K D
authors.initials: KD
authors.lastname: Cotton
authors.forename: M A
authors.initials: MA
authors.lastname: Hollywood
authors.forename: N G
authors.initials: NG
authors.lastname: McHale
authors.forename: K D
authors.initials: KD
authors.lastname: Thornbury
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D005260:Female; D066298:In Vitro Techniques; D008208:Lymphatic System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009183:Mycotoxins / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D012756:Sheep; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009183:Mycotoxins; D010455:Peptides; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; C003626:tremortin; D019789:Tetraethylammonium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C064719:iberiotoxin; D015761:4-Aminopyridine; D009543:Nifedipine