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- Title
Distribution of K[sup+]-Dependent Na[sup+]/Ca²+; Exchangers in the Rat Supraoptic Magnocellular Neuron Is Polarized to Axon Terminals.
- Authors
Myoung-Hwan Kim, Toshihiko; Sang-hyuk Lee, Toshihiko; Kyeong Han Park, Toshihiko; Won-Kyung Ho; Suk-Ho Lee
- Abstract
Neurons are polarized into compartments such as the soma, dendrites, and axon terminals, each of which has highly specialized functions. To test whether Ca&sup2+; is differently handled in different compartments of a neuron, we investigated Ca&sup2+; clearance mechanisms in somata of supraoptic magnocellular neurosecretory cells (MNCs) and in their axon terminals located in neurohypophyses. Using patch-clamp and microfluorometry techniques, Ca&sup2+; transients were evoked by depolarizing pulses. Endogenous Ca&sup2+; binding ratios (κ[subS]) and Ca&sup2+; clearance rates were calculated from the decay phases of Ca&sup2+; transients according to the single compartment model. Mean values of κ[subS] were 79 ± 2.6 in somata of MNCs and 187 ± 19 in axon terminals. Ca&sup2+; clearance rate in axon terminals, which were calculated from time derivative of Ca&sup2+; decay and the κ[subS] values, were approximately threefold higher than in somata. In response to external Na[sup+] reduction, Ca&sup2+; clearance rates were reduced by 65% in axon terminals, but did not change in somata. Immunohistochemical assays confirmed that K[sup+]-dependent Na[sup+]/Ca&sup2+; exchanger (NCKX2) was specifically localized to neurohypophysial axon terminals and was not found in somata. In somata, inhibition of sarcoendoplasmic reticulum Ca&sup2+;-ATPase (SERCA) pumps, mitochondrial Ca&sup2+;-uniporter, and plasma membrane Ca&sup2+;-ATPase (PMCA) pumps decreased Ca&sup2+; clearance rate by 48, 27, and 21%, respectively. These results suggest that neurohypophysial axon terminals have greater Ca&sup2+; clearance power than somata because of the specific localization of NCKX2, and that Ca&sup2+; clearance in somata of MNCs is mediated by SERCA pumps, mitochondrial uniporter, and PMCA pumps.
- Subjects
NEURONS; AXONS; DENDRITES; CELLS; NEUROSCIENCES
- Publication
Journal of Neuroscience, 2003, Vol 23, Issue 37, p11673
- ISSN
0270-6474
- Publication type
Article
- DOI
10.1523/JNEUROSCI.23-37-11673.2003