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J Physiol Vol 242, Issue 2 pp 453-470
Copyright © 1974 by The Physiological Society
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Intracellular chloride activity and the effects of acetylcholine in snail neurones

 T. O. Neild and R. C. Thomas

1. Cl--sensitive micro-electrodes were used to measure intracellular Cl- in snail neurones. The electrodes consisted of a sharpened and chlorided silver wire mounted inside a glass micropipette.

2. The electrodes appeared to record changes in internal Cl- accurately but in H cells the chloride equilibrium potential (ECl) as measured by the Cl--sensitive electrode was always less negative than EACh.

3. In some H cells ACh caused a measurable increase in internal Cl- when the cell was at its resting potential. In voltage-clamped cells there was a close correlation between the change in internal Cl- and the extra clamp current caused by a brief application of ACh. This confirmed that ACh increases the cell's membrane permeability only to Cl- ions, and that EACh was equal to ECl.

4. There was good agreement between the measured change in internal Cl- and that calculated from the cell size and clamp charge only when it was assumed that a constant voltage offset was added to the potential of the Cl--sensitive electrode while it was inside the nerve cell.

5. Cl--sensitive electrodes with AgCl as the sensitive material appear to be unsuitable for intracellular measurement of Cl-, although they might be suitable for following changes in ECl.

6. In certain D cells ACh also caused an increase in internal Cl- although it decreased the membrane potential. In the presence of hexamethonium, ACh caused a hyperpolarization and a smaller increase in internal chloride.

7. It is concluded that the intracellular Cl- in both H and D cells is about 8·3 mM, giving an ECl of about -58 mV.






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