Histamine (HIS), a neurotransmitter in a number of invertebrates rarely has been reported in bivalves. We showed in the bivalve Crassostrea virginica HIS is involved in sensory reception in regulation of gill lateral cell cilia beating, quantified HIS in ganglia and tissues and visualized HIS and HIS H2 receptors in tissues, including gill interfilamental junctions (IFJ). We hypothesize HIS H2 receptors can be confirmed by Western Blot and HIS has a physiological role at gill IFJ. For Western Blot, gill cell lysate was prepared by polytron disruption in NP-40 detergent buffer containing protease inhibitor and centrifuged to obtain supernatant with solubilized membrane proteins. Up to 30 µg of protein was subjected to SDS-PAGE with 10% acrylamide gels and electroblotted onto nitrocellulose. H2 receptor immunoreactivity was revealed by incubation with H2 1 antibodies then incubation with HRP-conjugated 2 antibodies. Gill H2 receptor protein was resolved by colormetric development using CN/DAB substrate ki...