Effects of TEA on hippocampal neurons.

The effects of the potassium channel blockers, tetraethylammonium (TEA) and tetramethylammonium (TMA) on behavior of hippocampal CA1 neurons were studied in the in vitro slice preparation. Intracellular injections of TEA produced marked spike broadening, increased input resistance, and a prolongation of a putative slow calcium-activated afterhyperpolization (AHP). Little effect was seen on synaptic potentials. Bursting activity induced by TEA in hippocampal neurons was qualitatively different from the epileptiform bursting induced by raising extracellular potassium concentrations or by including penicillin in the bathing medium. Effects of TMA were qualitatively similar to those of TEA, but much slower and less dramatic. The results suggested that there were at least two different potassium channels in the membranes of hippocampal CA1 neurons, and that both were important in determining normal neuronal activity. TEA appeared to preferentially block a fast, voltage-dependent potassium conductance (gk); however, it also modified the slow, calcium-activated gk. Although cell bursting activity may have resulted from blockade of a gk produced by TEA treatment, the epileptiform bursts produced by penicillin exposure appeared to be independent of this mechanism.