Targeted disruption of the Nhe1 gene fails to inhibit beta(1)-adrenergic receptor-induced parotid gland hypertrophy.

Chronic beta(1)-adrenergic receptor activation results in hypertrophy and hyperplasia of rodent salivary gland acinar cells. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates cell volume and the induction of cell proliferation in many tissues. To investigate the relationship between NHE1 and the response of parotid glands to beta(1)-adrenergic agonists, we examined by Northern blot analysis NHE1 expression in saline-treated mice and mice 30 min and 2, 6, and 24 h after isoproterenol injection. NHE1 transcripts increased approximately 50% by 2 h, and a more than twofold increase was noted at 24 h. Isoproterenol did not acutely increase Na(+)/H(+) exchanger activity; however, exchanger activity was significantly elevated by 24 h. To test whether NHE1 activity is essential for inducing salivary gland hypertrophy in vivo, mice with targeted disruption of Nhe1 were treated with isoproterenol. Na(+)/H(+) exchanger activity was absent in acinar cells from Nhe1(-/-) mice, nevertheless, the lack of NHE1 failed to inhibit isoproterenol-induced hypertrophy. These data directly demonstrate that acinar cell hypertrophy induced by chronic beta(1)-adrenergic receptor stimulation occurs independently of NHE1 activity.