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Ca 2+ current and Ca 2+ ‐activated chloride current in isolated smooth muscle cells of the sheep urethra
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.1469-7793.1997.121bc.x
Subject(s) - niflumic acid , chemistry , depolarization , biophysics , reversal potential , chloride channel , patch clamp , current clamp , nifedipine , membrane potential , tetraethylammonium chloride , channel blocker , chloride , voltage clamp , calcium , biochemistry , potassium , biology , receptor , organic chemistry
1 Isolated sheep urethral cells were studied using the perforated patch clamp technique ( T = 37 °C). Depolarizing steps ranging from ‐40 to ‐10 mV evoked an inward current that peaked within 10 ms and a slower inward current. Stepping back to the holding potential of ‐80 mV evoked large inward tail currents. All three currents were abolished by nifedipine (1 μ m ). Substitution of external Ca 2+ with Ba 2+ resulted in potentiation of the fast inward current and blockade of the slow current and tails. 2 Changing the chloride equilibrium potential ( E Cl ) from 0 to + 27 mV shifted the reversal potential of the tail currents from 1 ± 1 to 27 ± 1 mV (number of cells, n = 5). Chloride channel blockers, niflumic acid (10 μ m ) and anthracene‐9‐carboxylic acid (9AC, 1 m m ), reduced the slow current and tails suggesting that these were Ca 2+ ‐activated CF currents, I Cl(Ca) . 4 Caffeine (10 m m ) induced currents that reversed at E Cl and were blocked by niflumic acid (10 μ m ). 5 In current clamp mode, some cells developed spontaneous transient depolarizations (STDs) and action potentials. Short exposure to nifedipine blocked the action potentials and unmasked STDs. In contrast, 9AC and niflumic acid reduced the amplitude of the STDs and blocked the action potentials. 6 In conclusion, these cells have both L‐type I Ca and I Cl(Ca) . The former appears to be responsible for the upstroke of the action potential, while the latter may act as a pacemaker current.