Asymmetrical distribution of G-proteins among the apical and basolateral membranes of rat enterocytes.
The distribution of the alpha and beta subunits of guanosine-nucleotide-binding proteins (G-proteins) among the apical and basolateral membranes of polarized rat enterocytes was investigated by ADP-ribosylation assays in vitro and immunoblotting with G-protein-subunit-specific antisera. The enterocytes were found to express alpha i2, alpha ji3, alpha s and beta subunits, whereas alpha i1 and alpha o subunits could not be detected. The alpha i2 and alpha i3 subunits were located predominantly in the basolateral membrane, in contrast with the alpha s and beta subunits, which were distributed uniformly among both membranes. Furthermore, 39 kDa and 78 kDa proteins, recognized by anti-alpha i1/2 but not anti-alpha i1 or anti-alpha i3 specific antisera, and resistant to ADP-ribosylation by pertussis toxin, were localized exclusively at the apical border. These Gi-related proteins might represent novel members of the G-protein family. Activation of apical G-proteins by GTP or its analogues failed to release the alpha s, alpha i and beta subunits or the 39 kDa and 78 kDa alpha i-like proteins from the membrane, suggesting a functional role for these proteins in the apical membrane itself. Our recent finding of a guanosine 5'-[gamma-thio]triphosphate-sensitive Cl- conductance in the apical membrane of rat enterocytes suggests that one or more of these G-proteins may act as local regulators of specific apical transport functions.
van den Berghe
N
N
Department of Biochemistry I, Erasmus University Rotterdam, The Netherlands.
Nieuwkoop
N J
NJ
Vaandrager
A B
AB
de Jonge
H R
HR
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001345:Autoradiography; D015153:Blotting, Western; D002384:Catalysis; D002772:Cholera Toxin / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007421:Intestine, Small / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D037342:Pertussis Toxin; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D008565:Membrane Proteins; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins