Premium
Membrane currents in cultured human intestinal smooth muscle cells
Author(s) -
Zholos A. V.,
Fenech C. J.,
Prestwich S. A.,
Bolton T. B.
Publication year - 2000
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.1469-7793.2000.00521.x
Subject(s) - chemistry , biophysics , depolarization , tetraethylammonium , cyclopiazonic acid , hyperpolarization (physics) , patch clamp , membrane potential , divalent , iberiotoxin , tetrodotoxin , repolarization , potassium channel , electrophysiology , intracellular , biochemistry , potassium , stereochemistry , biology , receptor , neuroscience , organic chemistry , nuclear magnetic resonance spectroscopy
1 Using whole‐cell patch‐clamp recording techniques, we have examined voltage‐gated ion currents in a cultured human intestinal smooth muscle cell line (HISM). Experiments were performed at room temperature on cells after passages 16 and 17. 2 Two major components of the whole‐cell current were a tetraethylammonium‐sensitive (IC 50 = 9 m m ), iberiotoxin‐resistant, delayed rectifier K + current and a Na + current inhibited by tetrodotoxin (IC 50 = 100 n m ). No measurable inward current via voltage‐gated Ca 2+ channels could be detected in these cells even with 10 m m Ca 2+ or Ba 2+ in the external solution. No current attributable to calcium‐activated K + channels was found and no cationic current in response to muscarinic receptor activation was present. 3 In divalent cation‐free external solution two additional currents were activated: an inwardly rectifying hyperpolarization‐activated current, I HA , and a depolarization‐activated current, I DA . 4 IHA and I DA could be carried by several monovalent cations; the sizes of currents in descending order were: K + > Cs + > Na + for I HA and Na + > K + >> Cs + for I DA . I HA was activated and deactivated instantaneously and showed no inactivation whereas I DA was activated, inactivated and deactivated within tens of milliseconds. These currents were inhibited by external calcium with an IC 50 of 0.3 μ m for I DA and an IC 50 of 20 μ m for I HA . 5 Cyclopiazonic acid (CPA) induced an outward, but not an inward current. SK&F 96365, a blocker of store‐operated Ca 2+ channels, suppressed I DA with a half‐maximal inhibitory concentration of 9 μ m but was ineffective in inhibiting I HA at concentrations up to 100 μ m . Gd 3+ and La 3+ strongly suppressed I DA at 1 and 10 μ m , respectively and were less effective in blocking I HA (complete inhibition required a concentration of 100 μ m for both). Carbachol at 10–100 μ m evoked about a 3‐fold increase in I HA amplitude and completely abolished I DA . 6 We conclude that I HA and I DA are Ca 2+ ‐blockable cationic currents with different ion selectivity profiles that are carried by different channels. I DA shows novel voltage‐dependent properties for a cationic current.