Co-ordinated expression of 5-HT sub(2C) receptors with the NCX1 Na super(+)/Ca super(2+) exchanger in histaminergic neurones

The different roles of Na super(+)/Ca super(2+) (NCX) exchangers and Na super(+)/Ca super(2+)/K super(+) (NCKX) exchangers in regulation of the ionic homeostasis in neurones are poorly understood. We have previously shown that serotonin excites histaminergic tuberomamillary (TM) neurones by activation of 5-HT sub(2C)-receptors and Na super(+)/Ca super(2+) exchange. With the help of single-cell RT-PCR (sc-RT-PCR) we have now determined the coexpression pattern of different subtypes of NCX and NCKX with serotonin receptors. The majority of TM neurones express NCX1, NCX2 and NCKX3. Serotonin 2C receptor-mRNA was detected in 70% while 5-HT sub(2A) mRNA was found in only 10% of TM neurones. In all neurones expressing the 5-HT sub(2C) receptor NCX1-mRNA was present. Double immunostaining revealed the presence of the NCX1 protein in histidine decarboxylase-positive neurones. In the majority of TM neurones one or two out of five isoforms, NCX1.4, NCX1.5, NCX1.7, NCX1.14, NCX1.15, were detected by cDNA sequencing and/or by restriction analysis. The alternative splicing region is important for the Ca super(2+) sensitivity and presumably for the modulation of NCX1 function by second messengers. We conclude that several exchanger-subtypes can be coexpressed in single neurones and that TM cells are heterogeneous with respect to their calcium homeostasis regulation.