PARRIE, Lindsay; TOWLE, David W.; Mt. Desert Island Biol. Lab., Salsbury Cove, ME: Induction of Na⁺+K⁺-ATPase α-subunit mRNA in branchial tissues of the American lobster Homarus americanus.

Lobsters of the genus Homarus are capable of osmoregulating in salinities as low as 15-20 ppt. Investigations on branchial chamber tissues of the European lobster Homarus gammarus suggest that the epipodites (thin structures separating the gills) and branchiostegite (vascularized tissue lining the branchial chamber) may be more important in this process than the gills themselves, unlike many other osmoregulating crustaceans. For example, long-term acclimation to dilute salinity leads to an increase in Na⁺+K⁺-ATPase activity in epipodites and branchiostegite but not gill. In addition, the epipodite epithelium is capable of active ion transport reflective of an osmoregulatory tissue. In this study, we identified and sequenced the α-subunit of the Na⁺+K⁺-ATPase in epipodite and antennal gland cDNA prepared from the American lobster Homarus americanus. The 4,159-nucleotide sequence contains an open reading frame that encodes a 1,039-amino-acid polypeptide with high homology to other crustacean α-subunit sequences. Real-time quantitative PCR analysis showed that short-term (0-48 h) acclimation to low salinity was accompanied by a substantial increase in α-subunit mRNA in epipodite, branchiostegite, and gill but not in antennal gland. Our results confirm the importance of epipodite and branchiostegite in the osmoregulatory response but suggest that the gills are involved as well. Supported by NSF DBI-0100394 and NIH BRIN 1P20RR16463-01.