Cytosolic pH affects DNA-synthesis in nasal gland cells of osmotically stressed ducklings, Anas platyrhynchos

Osmotic stress in ducklings (Anas platyrhynchos) results in adaptive cell p roliferation in the salt-excretory nasal glands. In this study, we have elu cidated the temporal relationship of voluntary salt-intake in ducklings to changes in body fluid osmolality and increases in DNA-synthesis rate as an indication for adaptive cell proliferation in the glands. In addition, expe riments using organo-typically cultured nasal gland tissue were performed t o test the previously raised hypothesis that cytosolic alkalinization may b e a regulatory factor in the onset of adaptive cell proliferation. The resu lts indicate that increases in body fluid osmolality in naive ducklings acc elerated DNA-synthesis in their nasal glands (measured as thymidine-incorpo ration rates in short-term tissue culture) with a lag period of 12 h and ma ximum values of 2.5 times the control between 14 and 24 h of osmotic stress . Experiments using intact animals and cultured nasal gland tissue revealed that amiloride, a substance blocking the Na/H-exchanger and preventing rec eptor-mediated cytosolic alkalinization in nasal gland cells, attenuated DN A-synthesis. Experimentally shifting the cytosolic pH in cultured tissue to the alkaline range by 0.1 units, however, resulted in a significant increa se in DNA-synthesis rate by more than 20 %. We conclude that cellular signa lling events triggering adaptive cell proliferation in secretory cells of t he duck salt gland are initiated within 12 h of osmotic stress. The previou sly described cytosolic alkalinization that occurs upon muscarinic activati on of nasal gland cells from naive (but not from previously stressed animal s) may be relevant in signalling processes mediating adaptive cell prolifer ation in nasal glands of osmotically stressed ducklings.