Activity of the unique beta-adrenergic Na+/H+ exchanger in trout erythrocytes is controlled by a novel beta3-AR subtype.
beta-Adrenoceptors (beta-ARs) are seven-transmembrane domain, G protein-coupled receptors that transduce the cellular effects of epinephrine and norepinephrine and play a pivotal role in the vertebrate stress response. This study reports the cloning and characterization of two previously unreported beta-ARs from the rainbow trout (Oncorhynchus mykiss). Phylogenetic analysis of amino acid sequences indicates that both beta-ARs are homologs of the mammalian beta3-AR. Analysis of tissue expression patterns indicates that one of these trout beta3-adrenoceptors (beta3a-AR) is highly expressed in gill and heart, whereas the second (beta3b-AR) is highly expressed by red blood cells (RBC). Expression of the beta3b-AR in the RBC coupled with the finding of a single category of beta-AR binding sites on RBC membranes provides strong evidence for the control of the trout RBC beta-AR Na+/H+ exchanger (beta-NHE) activity by signaling through this beta3b-subtype and not through a beta1-subtype as previously proposed. The RBC-specific trout beta3b-AR exhibits binding characteristics that distinguish this receptor from each of the three pharmacologically defined categories of mammalian beta-ARs (beta1-, beta2-, and beta3-AR). This study is the first to report the presence of a beta3-AR subtype in a fish species, and the proposal that the beta3b-AR controls RBC beta-NHE activity represents a novel role for the beta3-AR subtype in vertebrates.
Nickerson
James G
JG
Dept. of Biology, Univ. of Ottawa, 150 Louis Pasteur, PO Box 450, Station A Ottawa, Ontario, Canada K1N 6N5.
Dugan
Stephen G
SG
Drouin
Guy
G
Perry
Steve F
SF
Moon
Thomas W
TW
D000818:Animals; D001483:Base Sequence; D001833:Body Temperature Regulation / Q000502:physiology; D004912:Erythrocytes / Q000378:metabolism; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000235:genetics*; D010802:Phylogeny; D022702:Receptors, Adrenergic, beta-3 / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism*
D022702:Receptors, Adrenergic, beta-3; D017923:Sodium-Hydrogen Exchangers