CHANNELS UNDERLYING THE SLOW AFTERHYPERPOLARIZATION IN HIPPOCAMPAL PYRAMIDAL NEURONS - NEUROTRANSMITTERS MODULATE THE OPEN PROBABILITY

The slow afterhyperpolarization in hippocampal pyramidal neurons is me diated by a calcium-activated potassium current (I-AHP) and is a targe t for a variety of different neurotransmitters. The characteristics of the channels underlying I-AHP and how they are modulated by neurotran smitters are, however, unknown. In this study, we have examined the pr operties of the channels underlying I-AHP using fluctuation analysis o f the macroscopic current. Our results indicate that this channel has a unitary conductance of 2-5 pS and a mean open time of about 2 ms. Wh en the peak amplitude of I-AHP was maximal, these channels have an ope n probability of 0.4. Noradrenaline and carbachol reduced I-AHP amplit ude by lowering open channel probability. These results indicate that a novel calcium-activated potassium channel underlies I-AHP. This chan nel is modulated in a similar fashion by two different transmitter sys tems that utilize distinct protein kinases.