Question #139

Which of the following manipulations would be expected to eliminate the early inward current in a voltage clamp experiment conducted on a piece of squid giant axon?

holding at a potential of -100 mV for 30 seconds prior to beginning the experiment

increasing the extracellular K+ concentration to 140 mM

treatment with tetraethylammonium (TEA)

treatment with curare

treatment with tetrodotoxin (TTX)

The early inward current seen in this setting follows through voltage activated Na+ channels. This component may be eliminated by any of the following measures:

1. blocking the channels with an agent such as TTX
2. inactivating the channels by holding at a depolarised extracellular potential (around +100 mV) for the period prior to conducting the experiment
3. altering either the intra- or extra-cellular Na+ concentrations such that they are equal

See A Thinking Approach to Physiology, pages 27 - 31.

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