Glucose transport stimulation by bradykinin in Swiss 3T3 fibroblasts: a pertussis toxin-sensitive mechanism operates without involvement of arachidonic acid and cyclic AMP

Possible role of arachidonic acid in the regulation of lactate production in rat Sertoli cells

The aim of the study was to determine whether arachidonic acid (AA) is involved in the regulation of Sertoli cell lactate production and if this fatty acid participates in follicle-stimulating hormone (FSH) regulation of Sertoli cell function. In a first set of experiments the effect of AA and porcine pancreas phospholipase A2 (PLA2) on lactate production, glucose uptake, lactate dehydrogenase (LDH) activity and LDH A mRNA levels in Sertoli cell cultures obtained from 20-day-old rats was evaluated. In a second set of experiments the effect of two PLA2 inhibitors--quinacrine (Q) and AACOCF3--on FSH stimulation of the above-mentioned parameters of Sertoli cell function was investigated. Treatment with PLA2 and AA increased Sertoli cell lactate production. The observed action of exogenously added PLA2 involved its catalytic properties responsible for AA release. PLA2 and AA treatments also stimulated Sertoli cell glucose uptake, LDH activity and LDH A mRNA levels. In order to determine whether AA participates in FSH regulation of Sertoli cell lactate production cells were incubated with FSH in the absence or presence of the PLA2 inhibitors Q and AACOCF3. Both drugs partially inhibited the ability of FSH to stimulate lactate production, glucose uptake and LDH activity. The present investigation suggests that AA is involved in the regulation of lactate production, glucose transport, LDH activity and LDH A mRNA levels. In addition, these results suggest that cytosolic PLA2 and AA may participate in FSH-regulation of Sertoli cell energetic metabolism.

The bradykinin B2 receptor is a delayed early response gene for platelet-derived growth factor in arterial smooth muscle cells

Bradykinin and platelet-derived growth factor (PDGF) are inflammatory mediators important in the response to vascular injury. Based upon the known effect of oncogenic Ras to increase bradykinin receptor expression and the ability of PDGF to stimulate Ras, we examined whether PDGF regulates bradykinin B2 receptor expression in cultured arterial smooth muscle cells. Treatment with PDGF (AB and BB, but not AA) produced a dose- and time-dependent increase in both mRNA (6-7-fold increase at 2-4 h) and cell surface receptors (2-4-fold at 6-12 h) for the B2 receptor. There was a 60-min delay between exposure to PDGF and the initial increase in B2 receptor mRNA. Transcriptional inhibitors, actinomycin D or 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole, completely blocked the increase in B2 receptor mRNA when added up to 60 min after stimulation with PDGF. However, protein synthesis was not required, as treatment with cycloheximide did not block but rather superinduced the PDGF-induced increase in B2 receptor mRNA. Comparison with the immediate early response gene c-fos demonstrated that the increase in B2 receptor mRNA was similarly inhibited by the tyrosine kinase inhibitor, tyrphostin, as well as staurosporine. However, stimulation of c-fos was slightly more sensitive to genistein, while the B2 receptor mRNA was more sensitive to inhibition by the protein kinase C inhibitor, calphostin C. The increase in cell surface B2 receptors were functionally coupled to an increase in phosphoinositide-specific phospholipase C, and the effects of PDGF were selective as there was no increase in either angiotensin II- or arginine vasopressin-induced inositol phosphate formation or intracellular calcium release. Taken together, these results demonstrate that the B2 receptor is a delayed early response gene for PDGF in vascular smooth muscle cells.

Interaction between growth factors and kinins in arterial smooth muscle cells

Bradykinin receptors are present on vascular smooth muscle cells; however, the regulation and biological function of these receptors is unclear. To address these questions the interaction between growth factors and kinins in cultured arterial smooth muscle cells has been examined. Based upon the data a hypothesis is presented that platelet-derived growth factor (PDGF) upregulates cell surface bradykinin B2 receptors on arterial smooth muscle cells. The biological effect of the increase in B2 receptors is currently unclear but under certain conditions they may enhance mitogenesis. These mitogenic effects however, are strongly opposed by the effects of bradykinin acting via a B1-type of receptor which mediates potent inhibition of growth factor-induced mitogenesis.

Arachidonic acid stimulates the intrinsic activity of ubiquitous glucose transporter (GLUT1) in 3T3-L1 adipocytes by a protein kinase C-independent mechanism

Exposure of adipocytes to arachidonic acid rapidly enhanced basal 2-deoxyglucose uptake, reaching maximal effect at approximately 8 hr. Insulin-stimulated 2-deoxyglucose uptake was not altered over the experimental period. While the short-term (2-h exposure) effect of arachidonic acid was negligibly influenced by cycloheximide, the enhancement of glucose transport by long-term (8-h) exposure to arachidonic acid was markedly decreased by the simultaneous presence of protein-synthesis inhibitors, implying that the short-term and long-term effects of arachidonic acid may involve distinct mechanisms. Immunoblot analysis revealed that 8-h but not 2-h exposure to arachidonic acid increased the content of the ubiquitous glucose transporter (GLUT1) in both total cellular and plasma membranes. The insulin-responsive glucose transporter (GLUT4), on the other hand, was not affected. Following 2-h exposure to arachidonic acid, kinetic studies indicated that the apparent Vmax of basal 2-deoxyglucose uptake was more than doubled, while the apparent Km for 2-deoxyglucose remained unchanged. Protein kinase C (PKC) depletion by pretreating cells with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) for 24 h had little influence on the subsequent enhancing effect of arachidonic acid on 2-deoxyglucose uptake. In addition, PMA was able to stimulate 2-deoxyglucose uptake in arachidonic-acid-pretreated cells with similar increments as in non-treated cells. Thus, our data seem to suggest that arachidonic acid may enhance the intrinsic activity of GLUT1 by a PKC-independent mechanism.

Bradykinin stimulates fructose 2,6-bisphosphate metabolism in human fibroblasts

Bradykinin (BK), a peptide released during inflammatory response, has been investigated for its ability to regulate glucose metabolism in human fibroblasts. The peptide is able to significantly increase glycolytic flux in these cells. The strict relationship between the glycolytic rate and the levels of fructose 2,6-bisphosphate (Fru-2,6-P2) strongly suggests that the metabolite plays a key role in the regulation of glucose metabolism by bradykinin. The mechanism by which bradykinin increases Fru-2,6-P2 content involves the activation of 6-phosphofructo-2-kinase (PFK-2), the enzyme responsible for the synthesis of the metabolite. The study of the multiple signalling systems triggered by bradykinin demonstrates the involvement of the rise in intracellular Ca2+ concentration and of protein kinase C mediated pathway in the mechanism by which bradykinin increases Fru-2,6-P2 content and PFK-2 activity.

Arachidonic acid stimulates glucose uptake in cerebral cortical astrocytes

Arachidonic acid (AA) has recently been shown to influence various cellular functions in the central nervous system. Here we report that AA increases, in a time- and concentration-dependent manner, 2-deoxy-D-[1-3H]glucose ([3H]2DG) uptake in primary cultures of astrocytes prepared from the cerebral cortex of neonatal mice. This effect is mimicked by an unsaturated fatty acid such as linolenic acid, while palmitic and arachidic acids, two saturated fatty acids, are inactive. Pharmacological agents that increase the endogenous levels of AA by stimulating AA release (melittin) or by inhibiting its reacylation (thimerosal) also promote [3H]2DG uptake by astrocytes. We also report that norepinephrine (NE) stimulates the release of [3H]AA from membrane phospholipids, with an EC50 of 3 microM; this effect is accompanied, with a temporal delay of approximately 4 min, by the stimulation of [3H]2DG uptake, for which the EC50 of NE is 1 microM. Since the cerebral cortex, the brain region from which astrocytes used in this study were prepared, receives a massive noradrenergic innervation, originating from the locus coeruleus, the effects of NE reported here further stress the notion that certain neurotransmitters may play a role in the regulation of energy metabolism in the cerebral cortex and point at astrocytes as the likely targets of such metabolic effects.