title: Distribution of K+-dependent Na+/Ca2+ exchangers in the rat supraoptic magnocellular neuron is polarized to axon terminals.
abstract: Neurons are polarized into compartments such as the soma, dendrites, and axon terminals, each of which has highly specialized functions. To test whether Ca2+ is differently handled in different compartments of a neuron, we investigated Ca2+ clearance mechanisms in somata of supraoptic magnocellular neurosecretory cells (MNCs) and in their axon terminals located in neurohypophyses. Using patch-clamp and microfluorometry techniques, Ca2+ transients were evoked by depolarizing pulses. Endogenous Ca2+ binding ratios (kappaS) and Ca2+ clearance rates were calculated from the decay phases of Ca2+ transients according to the single compartment model. Mean values of kappaS were 79 +/- 2.6 in somata of MNCs and 187 +/- 19 in axon terminals. Ca2+ clearance rate in axon terminals, which were calculated from time derivative of Ca2+ decay and the kappaS values, were approximately threefold higher than in somata. In response to external Na+ reduction, Ca2+ clearance rates were reduced by 65% in axon terminals, but did not change in somata. Immunohistochemical assays confirmed that K+-dependent Na+/Ca2+ exchanger (NCKX2) was specifically localized to neurohypophysial axon terminals and was not found in somata. In somata, inhibition of sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) pumps, mitochondrial Ca2+-uniporter, and plasma membrane Ca2+-ATPase (PMCA) pumps decreased Ca2+ clearance rate by 48, 27, and 21%, respectively. These results suggest that neurohypophysial axon terminals have greater Ca2+ clearance power than somata because of the specific localization of NCKX2, and that Ca2+ clearance in somata of MNCs is mediated by SERCA pumps, mitochondrial uniporter, and PMCA pumps.
authors.affiliation: Department of Physiology, Seoul National University College of Medicine, Chongno-Ku, Seoul, 110-799, Korea.
authors.forename: Myoung-Hwan
authors.initials: MH
authors.lastname: Kim
authors.forename: Sang-Hyuk
authors.initials: SH
authors.lastname: Lee
authors.forename: Kyeong Han
authors.initials: KH
authors.lastname: Park
authors.forename: Won-Kyung
authors.initials: WK
authors.lastname: Ho
authors.forename: Suk-Ho
authors.initials: SH
authors.lastname: Lee
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D016764:Cell Polarity; D002478:Cells, Cultured; D017136:Ion Transport; D008297:Male; D009474:Neurons / Q000737:chemistry* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010904:Pituitary Gland, Posterior / Q000166:cytology; D017729:Presynaptic Terminals / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000032:analysis* / Q000502:physiology; D013495:Supraoptic Nucleus / Q000737:chemistry* / Q000166:cytology
chemical_list: D019831:Sodium-Calcium Exchanger; C074530:potassium-dependent sodium-calcium exchanger; D002118:Calcium