Date of Award


Document Type


Degree Name

Master of Science



First Advisor

Dr. David W. Towle

Second Advisor

Dr. Francis B. Leftwich

Third Advisor

Dr. Warwick R. West, Jr.


Na+/H+ exchange was studied in plasma membrane vesicles from gills of three species of crabs: Callinectes sapidus (blue crab), Libinia dubia (spider crab), and Menippe mercenaria (stone crab). Spider crabs and stone crabs were acclimated to full (35ppt) seawater, while blue crabs were acclimated to both dilute (5ppt) and full strength seawater. Membrane vesicles were prepared by sucrose density centrifugation. Na+/H+ exchange was analyzed using acridine orange fluorescence. Male C. sapidus showed the most exchange activity (per g gill tissue), followed by M. mercenaria, female C. sapidus and Libinia dubia. No difference in exchange activity was evident when blue crabs were acclimated to both full and dilute seawater. The Na+/H+ exchange stoichiometry was larger than one for both C. sapidus and M. mercenaria, but approximately one for L. dubia. C. sapidus is an osmoregulator and can move from high salinities to reduced; its exchange mechanism may be more efficient in obtaining Na+ from lower salinities, compared to the stenohaline L. dubia. The control of ionic exchange in gills of M. mercenaria has not been studied. However, a stoichiometry as well as exchange rate similar to C. sapidus would suggest that some regulation is possible.

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