Outward currents in smooth muscle cells isolated from sheep mesenteric lymphatics

Cotton, K. D. and Hollywood, Mark A. and McHale, Noel G. and Thornbury, Keith D. (1997) Outward currents in smooth muscle cells isolated from sheep mesenteric lymphatics. J Physiol. , 503 (1). pp. 1-11.

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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.

Item Type: Article
Uncontrolled Keywords: 3-Pyridinecarboxylic acid; 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl); Methyl ester/pharmacology ; 4-Aminopyridine/pharmacology; Animals; Calcium Channel Blockers/pharmacology; Calcium Channels/physiology; Female; Lymphatic System/drug effects; Lymphatic System/physiology; Male; Membrane Potentials/drug effects; Membrane Potentials/physiology; Muscle, Smooth/drug effects; Muscle, Smooth/physiology; Mycotoxins/pharmacology; Nifedipine/pharmacology; Patch-Clamp Techniques; Peptides/pharmacology; Potassium Channels/physiology; Sheep; Tetraethylammonium; Tetraethylammonium Compounds/pharmacology
Subjects: Science
Research Centres: Smooth Muscle Research Centre
Depositing User: Concepta Woods
Date Deposited: 08 Mar 2012 16:41
Last Modified: 11 Nov 2014 16:10

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