title: Ca(2+)-activated Cl(-) current in sheep lymphatic smooth muscle.
abstract: Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37 degrees C using the perforated patch-clamp technique with Cs(+)- and K(+)-filled pipettes. Depolarizing steps evoked currents that consisted of L-type Ca(2+) [I(Ca(L))] current and a slowly developing current. The slow current reversed at 1 +/- 1.5 mV with symmetrical Cl(-) concentrations compared with 23.2 +/- 1.2 mV (n = 5) and -34.3 +/- 3.5 mV (n = 4) when external Cl(-) was substituted with either glutamate (86 mM) or I(-) (125 mM). Nifedipine (1 microM) blocked and BAY K 8644 enhanced I(Ca(L)), the slow-developing sustained current, and the tail current. The Cl(-) channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl(-) equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca(2+)-activated Cl(-) current plays an important role in the electrical activity underlying spontaneous activity in this tissue.
authors.affiliation: Smooth Muscle Group, Department of Physiology, Queen's University, Belfast BT9 7BL, United Kingdom.
authors.forename: H M
authors.initials: HM
authors.lastname: Toland
authors.forename: K D
authors.initials: KD
authors.lastname: McCloskey
authors.forename: K D
authors.initials: KD
authors.lastname: Thornbury
authors.forename: N G
authors.initials: NG
authors.lastname: McHale
authors.forename: M A
authors.initials: MA
authors.lastname: Hollywood
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D004553:Electric Conductivity; D005260:Female; D007425:Intracellular Membranes / Q000378:metabolism; D007477:Ions; D008208:Lymphatic System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012756:Sheep
chemical_list: D000873:Anthracenes; D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D018118:Chloride Channels; D007477:Ions; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C010030:9-anthroic acid; D009543:Nifedipine; D002118:Calcium