Stretch-activated cation channel TRPV4 mediates hyposmotically induced prolactin release from prolactin cells of mozambique tilapia Oreochromis mossambicus

Abstract

In teleost fish, prolactin (PRL) is an important hormone for hyperosmoregulation. The release of PRL from the pituitary of Mozambique tilapia is stimulated by a decrease in extracellular osmolality. Previous studies have shown that hyposmotically induced PRL release is linked with cell volume changes, and that stretch-activated Ca(2+) channels are likely responsible for the initiation of the signal transduction for PRL release. In this study, we identified the stretch-activated Ca(2+) channel transient receptor potential vanilloid 4 (TRPV4) from the rostral pars distalis (RPD) of tilapia acclimated to freshwater (FW). TRPV4 transcripts were ubiquitously expressed in tilapia; the level of expression in RPDs of FW-acclimated fish was lower than that found in RPDs of seawater (SW)-acclimated fish. Immunohistochemical analysis of the pituitary revealed that TRPV4 is localized in the cell membrane of PRL cells of both FW and SW tilapia. A functional assay with CHO-K1 cells showed that tilapia TRPV4 responded to a decrease in extracellular osmolality, and that its function was suppressed by ruthenium red (RR) and activated by 4α-phorbol 12,13-didecanoate (4aPDD). Exposure of dissociated PRL cells from FW-acclimated tilapia to RR blocked hyposmolality induced PRL release. PRL release, on the other hand, was stimulated by 4aPDD. These results indicate that PRL release in response to physiologically relevant changes in extracellular osmolality is mediated by the osmotically sensitive TRPV4 cation channel.

Gill Transcriptome Sequencing and De Novo Annotation of Acanthogobius ommaturus in Response to Salinity Stress

“…Prolactin ( PRL ) is a freshwater adapting hormone in teleosts that acts by reducing water permeability and promoting ion uptake by osmoregulatory organs, such as gills [ 61 ]. PRL release in a hypoosmotic environment is induced by an increase in PRL cell volume brought about by the influx of water via a membrane-bound AQP3 [ 62 ] and Ca 2+ influx through the stretch-activated channel TRPV4 [ 63 ]. PRL may play an important role in the control of water and electrolyte balance through PRLR expressed in the osmoregulatory organs in the marine teleost [ 64 ].…”

Hormonal regulation of aquaporin 3: opposing actions of prolactin and cortisol in tilapia gill

“…For example, the inhibition of Aqp3-mediated water movement by mercury treatment abolished the osmotically driven cell volume increases that follow reductions in extracellular osmolality (Watanabe et al 2009). These cell volume changes are essential to coupling extracellular conditions with appropriate Prl release via the stretch-activated Ca 2+ channel, transient receptor potential vanilloid 4 (Seale et al 2003, Watanabe et al 2012. Therefore, if the presumed role of branchial Aqp3 is to facilitate changes in cell volume, as in the pituitary, then Prl may play a key role in supporting osmosensitivity in the gill via Aqp3.…”

Tilapia (Oreochromis mossambicus) brain cells respond to hyperosmotic challenge by inducingmyo-inositol biosynthesis

“…Some other aspects of the neuroendocrine response to osmotic challenge in tilapia, such as prolactin release, have also been reported to be stimulated under changing plasma osmolality (Seale et al, 2006). Interestingly, prolactin cells of freshwater-acclimated tilapia are more sensitive to changes in osmolality than prolactin cells of saltwater-acclimated fish (Seale et al, 2012b;Watanabe et al, 2012). The osmotic sensitivity of tilapia brain cells (neurons and glia) has not yet been investigated in response to changes in extracellular osmolality.…”