Chloride Currents in Skeletal Muscles of Bufo arenarum |
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Authors: | G Bertrán BA Kotsias |
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Institution: | (1) Instituto de Investigaciones Médicas A. Lanari (UBA), Donato Alvarez 3150, 1427 Buenos Aires, Argentina, AR |
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Abstract: | Cl− currents (I
Cl) were measured in short fibers (1–2 mm) from the lumbricalis muscle of toads (Bufo arenarum) with two microelectrodes (15°C). Initially the fibers were equilibrated in a high K+-containing solution: (mm) K2SO4 68; Na2SO4 20; KCl 60; CaSO4 8; MgSO4 1; HEPES 2.5. Constant pulses were applied when all the external K+ was replaced by Cs+: Cs2SO4 68; Na2SO4 20; CsCl 60; CaSO4 8; HEPES 2.5 (pH 7.5). Under these conditions about 80–90% of the current is carried by Cl−. The current-voltage relation is almost linear implying constant conductance and hence voltage-independent permeability.
The voltage dependence of the net Cl− current could be fitted by constant field equation with a P
Cl of 3.3 × 10−6 cm/sec. In a separate group of experiments a two-pulse technique was used to estimate the availability and the inactivation
of the initial I
Cl during a test pulse. After returning the potential to the holding potential for various times, test pulses of the same amplitude
and duration of the prepulses were applied. The initial current during the test pulse was 70% of the initial current during
the prepulse and the recovery was complete in less than 300 msec with a linear relationship between the current during the
test pulse and the amplitude of the preceding prepulse. When the test pulses were preceded by a positive prepulse, the initial
current for any given test pulse was larger than with a negative prepulse. If we assumed that the initial current during the
test pulse is a measure of the number of channels open at the end of the prepulse, these results suggest that hyperpolarizing
pulses inactivate and depolarizing prepulses activate the I
Cl.
Received: 31 March 1995/Revised: 27 October 1995 |
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Keywords: | : Toad muscles — Skeletal muscle — Chloride currents — Muscle membrane — Voltage-clamped fibers |
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