Failure to up-regulate gill Na+,K+-ATPase alpha-subunit isoform alpha1b may limit seawater tolerance of land-locked Arctic char (Salvelinus alpinus).

ABSTRACT

Many populations of Arctic char (Salvelinus alpinus) are land-locked, physically separated from the ocean by natural barriers and unable to migrate to sea like anadromous populations. Previous studies which experimentally transferred land-locked Arctic char to seawater report high mortality rates due to osmoregulatory failure and an inability to up-regulate gill Na(+),K(+)-ATPase activity. This study examined the mRNA expression of two recently discovered alpha-subunit isoforms of gill Na(+)K(+)-ATPase (alpha1a and alpha1b) during seawater exposure of land-locked Arctic char. mRNA levels of these gill Na(+),K(+)-ATPasealpha-subunit isoforms were compared to Na(+),K(+)-ATPase activity and protein levels and related to osmoregulatory performance. Land-locked Arctic char were unable to regulate plasma osmolality following seawater exposure. Seawater exposure did not induce an increase in gill Na(+),K(+)-ATPase activity or protein levels. Na(+),K(+)-ATPase isoform alpha1a mRNA quickly decreased upon exposure to seawater, while isoform alpha1b levels were unchanged. These results suggest the inability of land-locked Arctic char to acclimate to seawater is due a failure to up-regulate gill Na(+),K(+)-ATPase activity which may be due to their inability to increase Na(+),K(+)-ATPase alpha1b mRNA expression.