Regulation of Na+/glucose cotransport in LLC-PK1 cells by glucose in culture medium: involvement of Gi protein.
The reduction of the glucose concentrations in the culture medium results in an increase in Na+/glucose cotransport activity in the epithelial cells. To study this regulation of Na+/glucose cotransport in LLC-PK1 cells, we have attempted to examine the involvement of Gi protein. The immunoblotting with an antibody for the carboxy-terminal of alpha subunit of Gi protein (Gi alpha) revealed no significant change in the level of Gi alpha in cells cultured with low (5 mM) or high (25 mM) glucose concentrations. In contrast, the cultured with low glucose concentrations induced the increases of both islet activating protein (IAP)-catalyzed ADP-ribosylation of Gi alpha and Na+/glucose cotransport activity. Furthermore, this increase in the transport activity was blocked by the presence of IAP in a dose dependent manner. These results suggest that there is a close relationship between the concentration of the heterotrimeric form of Gi protein (Gi alpha beta gamma) and the activity of Na+/glucose cotransport in LLC-PK1 cells.
Maruo
J
J
Department of Physiological Chemistry, Hiroshima University School of Medicine, Japan.
Kurokawa
T
T
Yasuda
H
H
Ishibashi
S
S
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D017077:Culture Media, Conditioned; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D013552:Swine
D017077:Culture Media, Conditioned; D015222:Sodium Channels; D000246:Adenosine Diphosphate Ribose; D019204:GTP-Binding Proteins; D005947:Glucose