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Multiple Pathways for High Voltage‐Activated C a 2+ Influx in Anterior Pituitary Lactotrophs and Somatotrophs
Author(s) -
Tzour A.,
Sosial E.,
Meir T.,
Canello T.,
NavehMany T.,
Gabizon R.,
Nussinovitch I.
Publication year - 2013
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.1365-2826.2012.02372.x
Subject(s) - prolactin cell , somatotropic cell , anterior pituitary , pituitary gland , endocrinology , medicine , blot , patch clamp , biology , channel blocker , chemistry , microbiology and biotechnology , receptor , biochemistry , gene , hormone , calcium
The present study demonstrates that a significant proportion of high voltage‐activated ( HVA ) C a 2+ influx in native rat anterior pituitary cells is carried through non‐ L ‐type C a 2+ channels. Using whole‐cell patch‐clamp recordings and specific C a 2+ channel toxin blockers, we show that approximately 35% of the HVA C a 2+ influx in somatotrophs and lactotrophs is carried through C a v 2.1, C a v 2.2 and C a v 2.3 channels, and that somatotrophs and lactotrophs share similar proportions of these non‐ L ‐type C a 2+ channels. Furthermore, experiments on mixed populations of native anterior pituitary cells revealed that the fraction of HVA C a 2+ influx carried through these non‐ L ‐type C a 2+ channels might even be higher (approximately 46%), suggesting that non‐ L ‐type channels exist in the majority of native anterior pituitary cells. Using western blotting, immunoblots for α 1C , α 1D , α 1A , α 1B and α 1E C a 2+ channel subunits were identified in native rat anterior pituitary cells. Additionally, using reverse transcriptase‐polymerase chain reaction, c DNA transcripts for α 1C , α 1D , α 1A and α 1B C a 2+ channel subunits were identified. Transcripts for α 1E were nonspecific and transcripts for α 1S were not detected at all (control). Taken together, these results clearly demonstrate the existence of multiple HVA C a 2+ channels in the membrane of rat native anterior pituitary cells. Whether these channels are segregated among different membrane compartments was investigated further in flotation assays, demonstrating that C a v 2.1, C a v 1.2 and caveolin‐1 were mostly localised in light fractions of N ycodenz gradients (i.e. in lipid raft domains). C a v 1.3 channels were distributed among both light and heavy fractions of the gradients (i.e. among raft and nonraft domains), whereas C a v 2.2 and C a v 2.3 channels were distributed mostly among nonraft domains. In summary, in the present study, we demonstrate multiple pathways for HVA C a 2+ influx through L ‐type and non‐ L ‐type C a 2+ channels in the membrane of native anterior pituitary cells. The compartmentalisation of these channels among raft and nonraft membrane domains might be essential for their proper regulation by separate receptors and signalling pathways.