Epinephrine regulates aquaglyceroporin HC‐3 expression and subcellular localization in cultured erythrocytes from the freeze‐tolerant treefrog, Hyla chrysoscelis (1099.5)

Abstract

Cope’s gray treefrog Hyla chrysoscelis, accumulates and distributes glycerol as a cryoprotectant in anticipation of freezing. Transmembrane glycerol and water flux in H. chysoscelis erythrocytes likely occurs through HC‐3, an ortholog of mammalian aquaporin 3. HC‐3 protein is in higher abundance and is preferentially localized to the plasma membrane in RBCs from cold‐acclimated treefrogs as compared to warm‐acclimated animals. It is hypothesized that neuroendocrine agonists via receptor mediated second messenger pathways integrate signals derived from fasting, dehydration, diurnal, and/or temperature changes during cold‐acclimation to regulate HC‐3 expression as part of the mechanism of freeze tolerance. In this study, cultured H. chrysoscelis erythrocytes were exposed to 1 uM epinephrine for 30 and 60 minutes. Native HC‐3 expression increased 3 fold at 30 minutes and 5.5‐fold at 60 minutes relative to controls, whereas glycosylated HC‐3 expression increased by 1.1‐fold at 30 minutes and by 2 ‐fold at 60 minutes relative when exposed to epinephrine. Moreover, epinephrine treatment resulted in membrane localization as compared to cytosolic distribution in control cells. Erythrocytes pre‐treated with Calphostin C, a PKC inhibitor, showed no HC‐3 membrane localization, and native HC‐3 expression was reduced by 66% relative to controls and 94% relative to epinephrine‐treated cells. Thus, epinephrine begins a PKC‐dependent mechanism that results in an increase in HC‐3 abundance, HC‐3 membrane localization, and enhanced glycosylation in erythrocytes. These regulatory mechanisms are consistent with the in vivo regulation of HC‐3 expression observed in erythrocytes from cold‐acclimated treefrogs.