EFFECTS OF PB2-RECTIFIER POTASSIUM CHANNELS IN ACUTELY ISOLATED HIPPOCAMPAL-NEURONS( ON DELAYED)

The effects of Pb2+ on delayed-rectifier potassium currents were studi ed in acutely isolated hippocampal neurons (CA1 neurons, CA3 neurons, granule cells) from the guinea pig using the patch-clamp technique in the whole cell configuration. Pb2+ in micromolar concentrations decrea sed the potassium currents in a voltage-dependent manner, which appear ed as a shift of the current-voltage relation to positive potentials. The effect was reversible after washing. The concentration-responsiven ess measured in CA1 neurons revealed an IC50 value of 30 mu mol/l at a potential of -30 mV. The half-maximal shift of the current-voltage re lation was reached at 33 mu mol/l and the maximal obtainable shift was 13.4 mV. For the different types of hippocampal neurons, the shift of the current-voltage relation was distinct and was 7.9 mV in CA1 neuro ns, 13.7 mV in CA3 neurons, and 14.2 mV in granule cells with 50 mu mo l/l Pb2+. The effects described here of Pb2+ on the potassium currents in hippocampal neurons and the differences between the types of hippo campal neurons correspond with the known properties and distributions of cloned potassium channels found in the hippocampus. As a whole, our results demonstrate that Pb2+ in micromolar concentration is a voltag e-dependent, reversible blocker of delayed-rectifier potassium current s of hippocampal neurons. This effect has to be taken into considerati on as a possible contributing mechanism for the neurological symptoms of enhanced brain activity seen during Pb2+ intoxication.