Serotonin and protein kinase C modulation of a rat brain inwardly rectifying K+ channel expressed in Xenopus oocytes

In Xenopus laevis oocytes injected with rat brain poly(A)(+) RNA, perfusion with a high-K+ solution (96 mM KCl) generated an inward current (I-HK) which was absent in water-injected oocytes. Part of I-HK was blocked by low concentrations of Ba2+ (half-maximal inhibitory concentration, IC50: 4.2 +/- 0.5 mu M). When serotonin (5-HT) was applied to these oocytes a transient inward oscillating Cl- current arising from activation of Ca2+-dependent Cl- channels, I-Cl(Ca), was observed. When this response decayed, a 30% reduction of I-HK could be detected. Electrophysiological characterization of the K+ channel down-modulated by 5-HT revealed that it is an inward rectifier. Antisense suppression experiments revealed that the 5-HT2C receptor mediates the down-modulatory effect of 5-HT. The nature of the modulatory pathway was investigated by application of phorbol esters and intracellular injection of protein kinase C (PKC) inhibitors, ethylenebis (oxonitrilo)tetraacetate (EGTA) and inositol 1, 4, 5-trisphosphate. The results demonstrate that PKC is responsible for the down-modulatory effect.