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The Expression of Voltage‐Gated Ca 2+ Channels in Pituicytes and the Up‐Regulation of L‐Type Ca 2+ Channels During Water Deprivation
Author(s) -
Wang D.,
Yan B.,
Rajapaksha W. R. A. K. J. S.,
Fisher T. E.
Publication year - 2009
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.2009.01906.x
Subject(s) - endocrinology , medicine , vasopressin , oxytocin , biology , chemistry
The primary components of the neurohypophysis are the neuroendocrine terminals that release vasopressin and oxytocin, and pituicytes, which are astrocytes that normally surround and envelop these terminals. Pituicytes regulate neurohormone release by secreting the inhibitory modulator taurine in an osmotically‐regulated fashion and undergo a marked structural reorganisation in response to dehydration as well as during lactation and parturition. Because of these unique functions, and the possibility that Ca 2+ influx could regulate their activity, we tested for the expression of voltage‐gated Ca 2+ channel α1 subunits in pituicytes both in situ and in primary culture. Colocalisation studies in neurohypophysial slices show that pituicytes (identified by their expression of the glial marker S100β), are immunoreactive for antibodies directed against Ca 2+ channel α1 subunits Ca V 2.2 and Ca V 2.3, which mediate N‐ and R‐type Ca 2+ currents, respectively. Pituicytes in primary culture express immunoreactivity for Ca V 1.2, Ca V 2.1, Ca V 2.2, Ca V 2.3 and Ca V 3.1 (which mediate L‐, P/Q‐, N‐, R‐ and T‐type currents, respectively) and immunoblotting studies confirmed the expression of these Ca 2+ channel α1 subunits. This increase in Ca 2+ channel expression may occur only in pituicytes in culture, or may reflect an inherent capability of pituicytes to initiate the expression of multiple types of Ca 2+ channels when stimulated to do so. We therefore performed immunohistochemistry studies on pituitaries obtained from rats that had been deprived of water for 24 h. Pituicytes in these preparations showed a significantly increased immunoreactivity to Ca V 1.2, suggesting that expression of these channels is up‐regulated during the adaptation to long‐lasting dehydration. Our results suggest that Ca 2+ channels may play important roles in pituicyte function, including a contribution to the adaptation that occurs in pituicytes when the need for hormone release is elevated.