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 α-subunit isoforms of gill Na +K +-ATPase (α1a and α1b) during seawater exposure of land-locked Arctic char. mRNA levels of these gill Na +,K +-ATPase α-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 α1a mRNA quickly decreased upon exposure to seawater, while isoform α1b 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 α1b mRNA expression.
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