Distinct perinatal features of the hyperpolarization-activated non-selective cation current I(h) in the rat cortical plate.
BACKGROUND
During neocortical development, multiple voltage- and ligand-gated ion channels are differentially expressed in neurons thereby shaping their intrinsic electrical properties. One of these voltage-gated ion channels, the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel and its current I(h), is an important regulator of neuronal excitability. Thus far, studies on an early I(h) appearance in rodent neocortex are missing or conflicting. Therefore, we focused our study on perinatal neocortical I(h) and its properties.


RESULTS
In the perinatal rat neocortex we observed a rapid increase in the number of neurons exhibiting I(h). Perinatal I(h) had unique properties: first, a pronounced cAMP sensitivity resulting in a marked shift of the voltage sufficient for half-maximum activation of the current towards depolarized voltages and second, an up to 10 times slower deactivation at physiological membrane potentials when compared to the one at postnatal day 30. The combination of these features was sufficient to suppress membrane resonance in our in silico and in vitro experiments. Although all four HCN subunits were present on the mRNA level we only detected HCN4, HCN3 and HCN1 on the protein level at P0. HCN1 protein at P0, however, appeared incompletely processed. At P30 glycosilated HCN1 and HCN2 dominated. By in silico simulations and heterologous co-expression experiments of a 'slow' and a 'fast' I(h) conducting HCN channel subunit in HEK293 cells, we mimicked most characteristics of the native current, pointing to a functional combination of subunit homo- or heteromeres.


CONCLUSIONS
Taken together, these data indicate a HCN subunit shift initiated in the first 24 hours after birth and implicate a prominent perinatal role of the phylogenetically older HCN3 and/or HCN4 subunits in the developing neocortex.
Institute of Cell Biology and Neurobiology, Center for Anatomy, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.
Arne
A
Battefeld
Nino
N
Rocha
Konstantin
K
Stadler
Anja U
AU
Bräuer
Ulf
U
Strauss
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D002461:Cell Line, Transformed; D002540:Cerebral Cortex / Q000166:cytology*; D003198:Computer Simulation; D000242:Cyclic AMP / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000037:antagonists & inhibitors / Q000145:classification / Q000235:genetics / Q000502:physiology*; D004558:Electric Stimulation; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008959:Models, Neurological; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D011743:Pyrimidines / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection
D054815:Cyclic Nucleotide-Gated Cation Channels; D004791:Enzyme Inhibitors; D004963:Estrenes; D011743:Pyrimidines; D011760:Pyrrolidinones; D012333:RNA, Messenger; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C082246:ICI D2788; D000242:Cyclic AMP; D002118:Calcium