UNEVEN DISTRIBUTION OF K- FUNCTIONAL-ROLE OF THE SOMA IN GENERATION OF ACTION-POTENTIALS( CHANNELS IN SOMA, AXON AND DENDRITES OF RAT SPINAL NEURONS )

1. A novel method of 'entire soma isolation' was used to describe the distribution of voltage-gated K+ channels between soma, axon and dendr ites of dorsal horn neurones identified in spinal cord slices of newbo rn rat. 2. The soma contained 36 % of total inactivating (K-A) current but only 15 % of delayed rectifier (K-DR) current. The axon initial s egment possessed almost half (47 %) of the total K-A current and 38% o f 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 some isolated from axon and dendrites was not able to generate act ion potentials. It passively conducted weak (less than or equal to-50m V) and amplified pronounced (-50 to 0 mV) depolarizations but inhibite d strong (greater than or equal to 0 mV) depolarizations. 4. It is con cluded that the soma plays a complex role in the excitability of spina l dorsal horn neurones. It conducts passively or amplifies excitatory postsynaptic potentials on their way from dendrites and soma to the ax on initial segment but it inhibits back-propagation of the action pote ntial from the axon to the dendrites.