Potassium channels in squid neuron cell bodies: comparison to axonal channels

The squid giant axon is formed from the fusion of many axons whose cell bodies are located in the giant fiber lobe (GFL) of the stellate ganglion. We measured macroscopic potassium channel currents in both squid giant axons and in the cell bodies. These currents appear similar in many ways, but were differently affected by the amino group modifying reagent, trinitrobenzene sulfonic acid (TNBS). TNBS increased the steady-state amplitude of the axonal currents but decreased the somal currents. We also studied single K channel currents in the giant fiber lobe cells, for comparison with single K channel currents measured previously in the axons. We found two common classes of K channels, distinguished by their conductances (11 and 25 pS) and kinetic properties. The two channel types resemble the 10 and 20 pS channels that have been described in squid giant axons. These results suggest that the cell bodies and axons express fundamentally similar K channel types. The different effects of amino group modification on macroscopic K currents in the two regions may arise from small (perhaps posttranslational) modifications of the core proteins.