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Tim M. Curtis, C. Norman Scholfield; Transient Ca2+-Activated Cl− Currents with Endothelin in Isolated Arteriolar Smooth Muscle Cells of the Choroid. Invest. Ophthalmol. Vis. Sci. 2000;41(8):2279-2285.
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purpose. To characterize the effects of endothelin (ET)-1 on the
Ca2+-activated Cl− conductance of choroidal
arteriolar smooth muscle.
methods. Microvascular smooth muscle cells were enzymatically isolated from
choroidal arterioles from the eyes of freshly killed rabbits. Cells
were voltage-clamped at −60 mV using the whole-cell perforated
patch-clamp technique. Internal pipette solutions were K+ based and contained amphotericin B (200 μg/ml). The cells were bathed
in a 20 mM tetraethyl–ammonium solution to block outward
results. Within 2 to 5 seconds of adding ET-1 (10 nM), inward current pulses
were generated at a frequency of around 1 Hz. These evoked transient
inward currents were blocked by niflumic acid (10 μM) or
anthracene-9-carboxylic acid (1 mM). They were increased 2.4 ±
0.1-fold when Cl− was replaced by I− in the
bathing medium and lost within 4 minutes when external Cl− was reduced from 151.6 to 20 mM. The reversal potential was −1 ±
2 mV with 135 mM Cl− in the recording pipette and with 54
mM Cl it was −18 ± 4 mV. When gramicidin D (100 μg/ml), which
maintains [Cl−]i, was used instead of
amphotericin B, the reversal potential was −18 ± 1 mV.
Ca2+ release by caffeine (10 mM) produced a single
transient inward current. Endothelin-evoked transient inward currents
were slowly reduced and eventually abolished in Ca2+-free
solution (∼2 to 3 minutes) and were eliminated after ∼30 seconds by
the sarcoplasmic reticulum Ca2+-uptake inhibitor
cyclopiazonic acid (5 μM). The ETA receptor antagonist
BQ123 (1 μM) prevented an effect by endothelin but did not inhibit
the current oscillations once they had been triggered.
conclusions. In choroidal arteriolar smooth muscle ET-1 evokes transient inward
Ca2+-activated Cl− currents induced through
the cyclical release and re-uptake of Ca2+ from
intracellular stores after ETA receptor
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