The possible role of cAMP and/or arachidonic acid (and metabolites) in the stimulation of glucose transport elicited by bradykinin in Swiss 3T3 fibroblasts was investigated with particular attention to the part of this effect inhibitable by pertussis toxin. Application of the membrane permeant cAMP analog 8-Br cAMP modified neither basal nor stimulated transport observed after bradykinin, insulin, or the combination of the two, indicating that [cAMP]i fluctuations are probably not involved. In contrast, arachidonic acid, which is released by the cells exposed to bradykinin, was able to markedly stimulate glucose transport, however, only at relatively high concentrations (EC50 ≈ 30 μM). The stimulation by arachidonic acid was insensitive to pertussis toxin and was largely inhibited by both the cyclooxygenase blocking drug, indomethacin, and the [Ca2+]i clamping at the resting level (by ionomycin administered in a Ca2+-free incubation medium). Neither of the last treatments affected the glucose transport activated by bradykinin to a great extent. Moreover, the bradykinin-induced arachidonic acid release was unaffected by pertussis toxin and markedly inhibited by two treatments ineffective on glucose transport, the blockade of [Ca2+]i increases elicited by the peptide and the administration of the phospholipase A2 blocker, quinacrine. These results exclude that glucose transport stimulation by bradykinin is mediated intracellularly via arachidonic acid release. Since the involvement of Ca2+ and diacylglycerol can also be ruled out by present and previous results , this effect of the peptide appears to be independent of the generation of known second messengers and might be triggered by the direct interaction of a pertussis toxin-sensitive G protein with the glucose transporter in the plane of the plasma membrane.
ASJC Scopus subject areas
- Cell Biology