HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 580/1/181    most recent jphysiol.2006.126680v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Zhang, W. Articles by Fisher, T. E. Search for Related Content PubMed PubMed Citation Articles by Zhang, W. Articles by Fisher, T. E. Related Collections Neuroscience

¹ Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5

The magnocellular neurosecretory cells of the hypothalamus (MNCs) regulate water balance by releasing vasopressin (VP) and oxytocin (OT) as a function of plasma osmolality. Release is determined largely by the rate and pattern of MNC firing, but sustained increases in osmolality also produce structural adaptations, such as cellular hypertrophy, that may be necessary for maintaining high levels of neuropeptide release. Since increases in Ca²⁺ current could enhance exocytotic secretion, influence MNC firing patterns, and activate gene transcription and translation, we tested whether Ca²⁺ currents in MNCs acutely isolated from the supraoptic nucleus (SON) of the hypothalamus are altered by 16–24 h of water deprivation. A comparison of whole-cell patch-clamp recordings demonstrated that dehydration causes a significant increase in the amplitude of current sensitive to the L-type Ca²⁺ channel blocker nifedipine (from –56 ± 6 to –99 ± 10 pA; P < 0.001) with no apparent change in other components of Ca²⁺ current. Post-recording immunocytochemical identification showed that this increase in current occurred in both OT- and VP-releasing MNCs. Radioligand binding studies of tissue from the SON showed there is also an increase in the density of binding sites for an L-type Ca²⁺ channel ligand (from 51.5 ± 4.8 to 68.1 ± 4.1 fmol (mg protein)^–1; P < 0.05), suggesting that there was an increase in the number of L-type channels on the plasma membrane of the MNCs or some other cell type in the SON. There were no changes in the measured number of binding sites for an N-type Ca²⁺ channel ligand. Dehydration was not associated with changes in the levels of mRNA coding for Ca²⁺ channel ₁ subunits. These data are consistent with the hypothesis that a selective increase of L-type Ca²⁺ current may contribute to the adaptation that occurs in the MNCs during dehydration.

(Received 14 December 2006; accepted after revision 11 January 2007; first published online 18 January 2007)
Corresponding author T. E. Fisher: Department of Physiology, College of Medicine, 107 Wiggins Road, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5. Email: thomas.fisher{at}usask.ca

This article has been cited by other articles:

				W. R. A. K. J. S. Rajapaksha, D. Wang, J. N. Davies, L. Chen, G. W. Zamponi, and T. E. Fisher Novel Splice Variants of Rat CaV2.1 That Lack Much of the Synaptic Protein Interaction Site Are Expressed in Neuroendocrine Cells J. Biol. Chem., June 6, 2008; 283(23): 15997 - 16003. [Abstract] [Full Text] [PDF]