Gonadotropin action on brook trout sperm duct epithelium: ion transport stimulation mediated by cAMP and Ca2+.
The isolated sperm duct epithelium from the brook trout Salvelinus fontinalis serves as a model for gonadotropin (GtH) action and is the only example of direct GtH stimulation of epithelial ion transport. In response to purified salmonid carbohydrate-rich GtH added to either the luminal or blood side of the epithelium, the duct actively secretes K+ (measured as 86Rb+ fluxes) and actively reabsorbs Na+ (measured by 22Na+ fluxes or as short circuit current, Isc). As a consequence of the ion transport, the seminal plasma has low Na+ concentration and high K+ content that in turn keeps developing sperm quiescent prior to spawning. All of the increase in Na+ transport in response to GtH addition can also be evoked by 1.0 mM db-cAMP + 0.1 mM 3-isobutyl-1-methylxanthine (IBMX), indicating that GtH action on Na+ transport is mediated by cAMP. In contrast, 86Rb+ efflux is only partially stimulated by db-cAMP + IBMX. K+ secretion can be stimulated fully by GtH or with the addition of the Ca2+ ionophore ionomycin (1 microM) in combination with db-cAMP + IBMX. Further, the cAMP-stimulated portion of K+ secretion is resistant to the K+ channel blocker Ba2+ (2.0 mM, added to the luminal side) while the ionomycin-stimulated K+ secretion is Ba(2+)- and quinidine (0.1 mM, luminal side)-sensitive. We conclude that GtH acts by two intracellular messengers in this system. The stimulation of Na+ active reabsorption and a Cl(-)-dependent K+ secretion are both mediated by cAMP. A second, Ba(2+)-sensitive K+ secretion is evoked by intracellular Ca2+ and likely represents a group of Ca(2+)-activated K+ channels on the apical membrane of the epithelium.
Marshall
W S
WS
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, Canada.
Bryson
S E
SE
Idler
D R
DR
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006062:Gonadotropins / Q000494:pharmacology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D012414:Rubidium Radioisotopes; D012474:Salmon / Q000378:metabolism*; D012671:Seminiferous Tubules / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D012979:Sodium Radioisotopes
D006062:Gonadotropins; D007473:Ion Channels; D015221:Potassium Channels; D012414:Rubidium Radioisotopes; D012979:Sodium Radioisotopes; D015759:Ionomycin; D003994:Bucladesine; D012964:Sodium; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine