Studies on functional properties of the inhibitory neurons in the hippocampus of the rat using slice-patch techniques and newly modified pr ocedur es.

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In dentate gyrus of the rat hippocampal slices, principal neurons (granule cells) and local inhibitory neurons (basket cells) identified under Namarsky microscopy. The effects of serotonin (5-HT) on these neurons were investigated using the whole-cell patch clamp technique and rapid perfusion (Y-tube) method. In granule cells, external application of 5-HT (0.2-100 uM) did not evoke any current but in basket cells definite inward currents at a holding potential of -63mV were induced. The I-V relation for 5-HT response showed a reversal potential around 0 mV accompanying a negative slope conductance at potentials below -60mV.To compare the functional proparties of these 5-HT receptors, newly identified ADP (adenosine-5'-diphosphate) receptors in the megakaryocytes from the mouse bone marrow were studied. When Cs^+ was used as a major internal cation to block K-currents, external application of ADP (10-100 uM) to dissociated megakaryocytes induced large inward currents (amplitude of 100-500 pA) at a holding potential of -42 mV,which showed a rapid decay with a complete inactivation in 1 sec.The amplitude of the ADP-induced currents became larger when hyperpolarized, while it became smaller by depolarization and reversed its polarity to outward at aroudn 0 mV.The overall I-V relationship showed an inward rectification. The ADP-induced inward currents are also observed in isotonic Ca2+ or Ba2+ or Mg2+ solution, which indicates that the channels activated by ADP are pormeable to these divalent cations. The channels are also permeable to monovalent cations such as Na+, K+ or Cs+.These indicate that a certain type of purinergic receptor is specifically involved in generating rapid cationic currents in megakaryocytes, the functional properties of which are very similar to those described for the 5-HT receptors in the brain.