Premium
Outward Currents in Smooth Muscle Cells Isolated from Sheep Mesenteric Lymphatics
Author(s) -
Cotton K. D.,
Hollywood M. A.,
McHale N. G.,
Thornbury K. D.
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.001bi.x
Subject(s) - tetraethylammonium , iberiotoxin , depolarization , biophysics , chemistry , membrane potential , patch clamp , reversal potential , nifedipine , charybdotoxin , myocyte , anatomy , repolarization , electrophysiology , potassium channel , endocrinology , medicine , calcium , biology , potassium , biochemistry , receptor , organic chemistry
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 μM) markedly reduced the outward current, while Bay K 8644 (1 μM) enhanced it. Up to 90% of the outward current was also blocked by iberiotoxin ( K d = 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 °C). The voltage required for half‐maximal activation of the channels ( V ½ ) shifted in the hyperpolarizing direction by 146 mV per 10‐fold increase in [Ca 2+ ] 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 ( V ½ =−41 ± 2 mV, slope factor = 18 ± 2 mV, 5 cells). 6 Tetraethylammonium (TEA; 30 mM) reduced the voltage‐dependent current by 75% ( K d = 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.