Summary
-
1.
The properties of a Ca-activated Cl-current ICl(Ca) were investigated with the two electrode voltage clamp technique in the AL1 cell of the leechHaementeria ghilianii.
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2.
ICl(Ca) was revealed after Cl-loading of the cells, with outward K-currents eliminated by replacement of intra- and extracellular K with Cs, and with Na currents blocked by 1μM TTX. CsCl-containing electrodes were used for recording and current passing.
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3.
In response to depolarizing voltage steps the cells exhibited sustained Cl-dependent currents the size and polarity of which varied with [Cl]0. The reversal potentials of tail currents of this conductance varied with [Cl]0 as predicted for the equilibrium potential of Cl by the Nernst equation and were unaffected by changes in extracellular cation concentration.
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4.
The decay of the Cl-dependent tail-currents followed a process which could be described by the sum of two exponentials with time constantsτ 1 andτ 2 on the order of about 100 ms and 800 ms, respectively. No voltage-dependence of the time constants was apparent; however,τ 1 varied with the amount of Ca-influx.
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5.
The Cl-current required Ca for its activation. All current flow was abolished in Mn-containing Ringer solutions and when Ba was substituted for Ca. However, Sr could partially substitute for Ca as an activator of the current.
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6.
The activation curve for Cl-dependent tail currents was U-shaped directly paralleling the amount of Ca-influx, and no Cl-current flow could be induced at depolarizations below the activation threshold or beyond the apparent reversal potential for the Ca-current.
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7.
ICl(Ca) was impermeable to large anions such as proprionate and acetate, but was permeable to both Br and Cl ions.
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Abbreviations
- TTX :
-
tetrodotoxin
- ICl(Ca) :
-
calcium-activated chloride current
- ICa :
-
calcium current
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Johansen, J., Kleinhaus, A.L. Voltage clamp characterization of a calcium-dependent chloride conductance in a putative invertebrate motoneuron. J. Comp. Physiol. 162, 57–65 (1988). https://doi.org/10.1007/BF01342703
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DOI: https://doi.org/10.1007/BF01342703