M. Seidelin et al., Expression of gill vacuolar-type H+-ATPase B subunit, and Na+, K+-ATPase alpha(1) and beta(1) subunit messenger RNAs in smolting Salmo salar, ZOOL SCI, 18(3), 2001, pp. 315-324
Changes in gill vacuolar-type H+-ATPase B subunit, and Na+,K+-ATPase alpha
and beta subunit mRNA expression were examined during the course of smoltif
ication in Salmo salar. We cloned and sequenced cDNA fragments of S. salar
gill i) vacuolar-type H+-ATPase (V-H+-ATPase) B subunit, ii) Na+,K+-ATPase
alpha (1) subunit, and iii) Na+,K+-ATPase beta (1) subunit, and used these
as Northern blotting probes. During smoltification, the salmon showed a typ
ical increase in gill Na+,K+-ATPase activity and improved hypo-osmoregulato
ry ability as judged by their ability to regulate plasma [Cl-] in a 24-hr s
eawater challenge test (35 ppt). Gill Na+,K+-ATPase alpha (1) and beta (1)
subunit mRNA levels were regulated at a constant ratio during smoltificatio
n. Both transcripts were elevated during the build-up of gill Na+,K+-ATPase
activity, underlining the importance of increased mRNA levels for increase
d enzyme activity. Gill V-H+-ATPase B subunit mRNA levels were high during
the early phase of smoltification. These results support our hypothesis tha
t gill V-H+-ATPase expression may be elevated during the early stages of sm
oltification in order to counter the effects of increased ionic efflux when
in FW. The peak smelt stage was, however, characterized by simultaneously
elevated gill Na+,K+-ATPase expression and low V-H+-ATPase expression, and
possibly ensures the complete transformation of the gill into a hypo-osmore
gulatory organ and hence the development of optimal SW-tolerance of the sme
lt.