Short- and long-term desensitization of serotonergic response in Xenopus oocytes injected with brain RNA: roles for inositol 1,4,5-trisphosphate and protein kinase C.
In Xenopus oocytes injected with rat brain RNA, serotonin (5HT) and acetylcholine (ACh) evoke membrane responses through a common biochemical cascade that includes activation of phospholipase C, production of inositol 1,4,5-trisphosphate (Ins1,4,5-P3), release of Ca2+ from intracellular stores, and opening of Ca-dependent Cl- channels. The response is a Cl- current composed of a transient component (5HT1 or ACh1) and a slow, long-lasting component (5HT2 or ACh2). Here we show that only the fast, but not the slow, component of the response is subject to desensitization that follows a previous application of the transmitter. The recovery of 5HT1 from desensitization is biphasic, suggesting the existence of two types of desensitization: short-term desensitization (STD), which lasts for less than 0.5 h; and long-term desensitization (LTD) lasting for up to 4 h. The desensitization between 5HT and ACh is heterologous and long-lasting. We searched for (a) the molecular target and (b) the cause of desensitization. (a) Pre-exposure to 5HT does not reduce the response evoked by intracellular injection of Ca2+ and by Ca2+ influx. Cl- current evoked by intracellular injection of Ins1,4,5-P3 was reduced shortly after application of 5HT, but fully recovered 30 min later. Thus, the Cl- channel is not a target for desensitization. Neither Ins1,4,5-P3 receptor nor the Ca2+ store is a target of LTD but they may be the targets of STD. (b) Ca2+ injection did not inhibit the 5HT response, suggesting that Ca2+ is not a sole cause of STD or LTD.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel.
D
D
Singer
R
R
Boton
O
O
Moran
N
N
Dascal
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001921:Brain; D002118:Calcium / Q000378:metabolism; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism; D005260:Female; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009865:Oocytes; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D012313:RNA / Q000378:metabolism*; D051381:Rats; D012701:Serotonin / Q000494:pharmacology*; D014981:Xenopus
D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D012701:Serotonin; D015240:Phorbol 12,13-Dibutyrate; D012313:RNA; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D000109:Acetylcholine; D002118:Calcium