PKC mediates GnRH activation of a Na+/H+ exchanger in goldfish somatotropes.
Previous results suggest that gonadotropin-releasing hormone (GnRH) stimulation of somatotropin secretion in goldfish involves activation of Na(+)/H(+) exchange (NHE). We tested the hypothesis that GnRH alkalinizes intracellular pH (pH(i)) via protein kinase C (PKC) activation of NHE. Two types of alkalinization responses were observed in identified goldfish somatotropes preloaded with the pH-sensitive dye BCECF; the rate of pH(i) changes went from a neutral or slightly negative slope to either a positive or a less negative slope relative to control. Two GnRHs, the PKC-activating TPA, and dioctanoyl glycerol each caused an alkalinization in 70-90% of somatotropes. The PKC inhibitors, Bis II and Gö6976, the NHE inhibitor amiloride, or Na(+)-free solution attenuated TPA and GnRHs actions, suggesting that PKC mediates GnRH activation of NHE. Since amiloride and Na(+)-free solution caused acidification in somatotropes at rest, regulation of basal pH(i) in these cells likely involves Na(+) flux through amiloride-sensitive NHE.
Li
Guang-Li
GL
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
Parks
Scott K
SK
Goss
Greg G
GG
Chang
John P
JP
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006054:Goldfish / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008297:Male; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism*; D052683:Somatotrophs / Q000201:enzymology / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D047428:Protein Kinase Inhibitors; D017923:Sodium-Hydrogen Exchangers; D007987:Gonadotropin-Releasing Hormone; D000584:Amiloride; D012964:Sodium; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate