PKC mediates GnRH activation of a Na+/H+ exchanger in goldfish somatotropes.

ABSTRACT

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.