Research: Presently,
the major focus of research is the control of feeding and respiration in
the northern quahog Mercenaria mercenaria. Both feeding and
respiration are a function of the amount of water flowing through the clam,
and water flow is regulated, in part, by the activity of cilia and muscle
fibers within the gill. We have been studying the control of these
effectors by the gill nerve net in addition to their modulation by endogenous
neuropeptides and the gaseous signaling molecules nitric oxide and hydrogen
sulfide. Not only are these gases produced by the gills, but they
occur naturally in seawater and marine sediments. Thus, in addition to
the details of the cell signaling pathways involved in control of the muscles
and cilia, one basic question that we hope to answer is how does
an animal use a signaling molecule that is also present in the environment
if the gases in the environment can freely enter the gill. Moreover, we
hope to understand how these gases affect water pumping in whole clams;
this question has important implications for the commercial production
of Mercenaria as a food source.
Collaborators: Dr. Michael
J. Greenberg, The C.V. Whitney Laboratory, The University of Florida (http://www.whitney.ufl.edu/research_programs/mgreenberg.htm)
and Dr. Shirley Baker, Institute of Food and Agricultural Sciences; The
University of Florida (http://fishweb.ifas.ufl.edu/Baker/Baker.htm).
Relevant Publications:
Gainey, Louis F, Jr., Kelly J.
Vining, Karen E. Doble, Jennifer M. Waldo, Aurora Candelario?Martinez,
and Michael J. Greenberg. 1999. An endogenous SCP-related peptide modulates
ciliary beating in the gills of a venerid clam Mercenaria mercenaria.
Biol. Bull. 197: 159-173.
Gainey, Louis F., Jr., James C.
Walton and Michael J. Greenberg. 2003. Branchial musculature of a venerid
clam: pharmacology,
distribution, and innervation.
Biol. Bull. 204: 81-95.
Gainey, Louis F., Jr. and Michael
J. Greenberg. 2003. Nitric oxide mediates seasonal muscle potentiation
in clam gills. J. Exp. Biol. 206:
3507-3520.
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Diagrammatic anatomy of Mercenaria
mercenaria: adapted from various sources on the basis of our own observations.
(A) A clam on the half shell. (B) Cross section of a clam. (C) Cross
section of a water tube: with the musculature relaxed (left), and contracted
(right). (D) Cross sections through portions of relaxed and contracted
demibranchs cut in an anterior-posterior direction, i.e. in and out of
the plane of the page with respect to B. Abbreviations: bv = blood vessel;
gf = gill filament; s= septum; wt = water tube; wtm = water tube
muscle; (Gainey & Greenberg, 2003; Gainey et al., 2003)
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Outer face of the gill with the muscles labeled
with green fluorescing phalloidin.
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Inner face of the gill with the muscles fluorescing
green.
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Inner face of the gill with the serontonergic
nerves fluorescing red.
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Outer face of the gill with muscles fluorescing
green and serontonergic nerves fluorescing red.
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