Calcium-activated chloride current in cultured sensory and parasympathetic quail neurones.

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RESUMO

1. Sensory (trigeminal and dorsal root) and autonomic (ciliary) ganglia from embryonic quail were dissociated and the neurones were grown in tissue culture. 2. Intracellular recordings were made in voltage clamp using patch electrodes and the whole-cell recording technique. In order to investigate a calcium-activated chloride current, the sodium and potassium currents were blocked. 3. Depolarizing voltage steps from a holding potential of -100 mV to a test potential of +20 mV triggered an early inward and a delayed outward current. The latter persisted as a long-lasting inward tail current when the membrane was depolarized to -100 mV. 4. These currents were all blocked by extracellular cobalt suggesting that they were calcium dependent. During a test depolarization to +20 mV, in the presence of intracellular EGTA (20 mM), the inward current persisted but the outward current was suppressed. EGTA (20 mM) also suppressed the long-lasting inward tail current at -100 mV. This suggested the presence of a calcium-activated current. 5. The reversal potential of the calcium-activated current was near the equilibrium potential for chloride ions and was shifted as predicted by the Nernst equation when the extracellular chloride concentration was changed. 6. The calcium-activated current was partially blocked by adding 4-acetamido-4'-isothiocyanatostilbene-disulphonic acid (SITS) at a concentration of 1 mM to the external superfusion medium. This effect of a compound known to interfere with chloride channels together with the results of point (5) suggested the existence of a calcium-activated chloride current (ICl(Ca)). 7. ICl(Ca) could be activated by transient and sustained components of the calcium current present in the cultured neurones. 8. ICl(Ca) was present in 80% of the sensory neurones but only in 10% of the parasympathetic neurones.

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