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Uneven distribution of K⁺ channels in soma, axon and dendrites of rat spinal neurones: functional role of the soma in generation of action potentials

Matthias Wolff, Werner Vogel and Boris V. Safronov

1. A novel method of 'entire soma isolation' was used to describe the distribution of voltage-gated K⁺ channels between soma, axon and dendrites of dorsal horn neurones identified in spinal cord slices of newborn rat.

2. The soma contained 36 % of total inactivating (K_A) current but only 15 % of delayed rectifier (K_DR) current. The axon initial segment possessed almost half (47 %) of the total K_A current and 38 % of K_DR current. In contrast, dendrites contained a small portion (17 %) of K_A but 47 % of K_DR current.

3. Under current-clamp conditions, the soma isolated from axon and dendrites was not able to generate action potentials. It passively conducted weak (<= -50 mV) and amplified pronounced (-50 to 0 mV) depolarizations but inhibited strong ( 0 mV) depolarizations.

4. It is concluded that the soma plays a complex role in the excitability of spinal dorsal horn neurones. It conducts passively or amplifies excitatory postsynaptic potentials on their way from dendrites and soma to the axon initial segment but it inhibits back-propagation of the action potential from the axon to the dendrites.

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