Biomedical subjects

B D Price

Publications and source records attributed to B D Price.

43 records · Page 3Linked to original sources

PubMed1989

Stimulation of phosphatidylcholine breakdown and diacylglycerol production by growth factors in Swiss-3T3 cells.

The effect of a number of growth factors on phosphatidylcholine (PtdCho) turnover in Swiss-3T3 cells was studied. Phorbol 12-myristate 13-acetate (PMA), bombesin, platelet-derived growth factor (PDGF) and vasopressin rapidly stimulated PtdCho hydrolysis, diacylglycerol (DAG) production, and PtdCho synthesis. Insulin and prostaglandin F2 alpha (PGF2 alpha) stimulated PtdCho synthesis, but not its breakdown, whereas epidermal growth factor (EGF) and bradykinin were without effect. Stimulation of PtdCho hydrolysis by the above ligands resulted in increased production of phosphocholine and DAG (due to phospholipase C activity) and significant amounts of choline, suggesting activation of a phospholipase D as well. CDP-choline and glycerophosphocholine levels were unchanged. Down-regulation of protein kinase C with PMA (400 nM, 40 h) abolished the stimulation of PtdCho hydrolysis and PtdCho synthesis by PMA, bombesin, PDGF and vasopressin, but not the stimulation of PtdCho synthesis by insulin and PGF2 alpha. PtdCho hydrolysis therefore occurs predominantly by activation of protein kinase C (either by PMA or PtdIns hydrolysis) leading to elevation of DAG levels derived from non-PtdIns(4,5)P2 sources. PtdCho synthesis occurs by both a protein kinase C-dependent pathway (stimulated by PMA, PDGF, bombesin and vasopressin) and a protein kinase C-independent pathway (stimulated by insulin and PGF2 alpha). DAG production from PtdCho hydrolysis is not the primary signal to activate protein kinase C, but may contribute to long-term activation of this kinase.

Animals↗

PubMed1989

Stimulation of phosphatidylcholine hydrolysis, diacylglycerol release, and arachidonic acid production by oncogenic ras is a consequence of protein kinase C activation.

Swiss-3T3 cells were scrape-loaded with oncogenically activated p21ras protein. 10-20 min after introducing Val12p21ras into the cell, diacylglycerol levels were increased, but levels of inositol phosphates were unaltered. However, cellular choline and phosphocholine levels were increased with a similar time course to that observed for diacylglycerol production, suggesting that ras increases phosphatidylcholine turnover but not phosphatidylinositol turnover. Down-regulation of protein kinase C (by prolonged exposure to phorbol esters prior to scrape loading) blocked the ability of ras protein to elevate the levels of diacylglycerol, choline, and phosphocholine. Oncogenic ras can, therefore, cause a substantial increase in diacylglycerol (which correlates with increased phosphatidylcholine breakdown) in a protein kinase C-dependent fashion. Val12p21ras also increased arachidonic acid release, which was also dependent on protein kinase C activation. Induction of DNA synthesis by oncogenic ras was unaffected by inhibitors of prostaglandin synthesis, indicating that conversion of the released arachidonic acid to various prostaglandins is not required for stimulation of DNA synthesis by ras. We suggest that ras rapidly activates protein kinase C, which in turn activates a number of cellular signalling systems, leading to a sustained increase in diacylglycerol levels. This elevation of diacylglycerol could sustain protein kinase C activation over the 12-15 h required for initiation of DNA synthesis.

Animals↗

PubMed1989

Scrape-loaded p21ras down-regulates agonist-stimulated inositol phosphate production by a mechanism involving protein kinase C.

The effect of scrape-loaded [Val-12]p21ras on agonist-stimulated phosphatidylinositol 4,5-bisphosphate (PIP2) turnover in Swiss-3T3 cells was studied. Previously [Morris, Price, Lloyd, Marshall & Hall (1989) Oncogene 4, 27-31] we demonstrated that [Val-12]p21ras activates protein kinase C within 10 min of scrape loading. Here, we show that [Val-12]p21ras inhibits bombesin and platelet-derived growth factor-stimulated PIP2 breakdown 1.5-4 h after scrape loading. This effect persisted for at least 18 h and could be mimicked in control cells by activation of protein kinase C with 12-O-tetradecanoyl 13-acetate (TPA) 15 min prior to ligand stimulation. When protein kinase C was down-regulated by chronic TPA treatment, [Val-12]p21ras was no longer able to inhibit agonist-stimulated inositol phosphate production. These results indicate that changes in inositol phosphate levels caused by ras protein are probably due to activation of protein kinase C and not to an interaction of ras with phospholipase C.

Animals↗

PubMed1985

Thermodynamic and steady-state-kinetic investigation of the effect of NN'-dicyclohexylcarbodi-imide on H+ translocation by the mitochondrial cytochrome bc1 complex.

Steady-state kinetic measurements showed that NN'-dicyclohexylcarbodi-imide decreased the observed H+/2e ratio of H+ transport by mitochondria respiring on succinate, acting mainly at the cytochrome bc1 complex. Thermodynamic assessment of the H+/2e ratio by measuring the force ratio across the bc1 complex showed that the inhibitor did not affect H+ translocation. Possible explanations of this disagreement between methods are examined; we conclude that the inhibitor does not alter the mechanistic stoichiometry of H+ pumping by the bc1 complex.

Animals↗

PubMed1983

Chemical modification of the mitochondrial bc1 complex by N,N'-dicyclohexylcarbodiimide inhibits proton translocation.

We report here that N,N'-dicyclohexylcarbodiimide (DCCD) decreases the H/2e stoichiometry of the cytochrome bc1 complex from 3.8 +/- 0.2 (10) to 2.1 +/- 0.1 (8) but has only a minimal effect on the H/2e ratio of cytochrome oxidase under the relatively mild conditions used. The effect on the bc1 complex cannot be explained by uncoupling, by inhibition of electron transport or by selective mitochondrial damage. We conclude that DCCD is an inhibitor of proton translocation within the bc1 complex. There are three possible explanations of this effect: (a) DCCD could alter the pathway of electron flow, (b) DCCD could prevent one of the proton translocation reactions but not electron transport, (c) DCCD could prevent the conduction of the translocated proton to the external phase.

Animals↗

PubMed1982

Proton translocation by the mitochondrial cytochrome b-c1 complex is inhibited by NN'-dicyclohexylcarbodi-imide.

NN'-Dicyclohexylcarbodi-imide at low concentrations decreases the H+/2e ratio for rat liver mitochondria over the span succinate to oxygen from 5.9 +/- 0.3 (mean +/- S.E.M.) to 4.0 +/- 0.1 and for the cytochrome b-c1 complex from 3.8 +/- 0.2 to 1.9 +/- 0.1, but has little effect on the H+/2e ratio of cytochrome oxidase. The decrease in stoicheiometry is due, not to uncoupling or inhibition of electron transport, but to inhibition of proton translocation. NN'-Dicyclohexylcarbodi-imide thus 'decouples' proton translocation in the cytochrome b-c1 complex.

Animals↗

PubMedDate not supplied

A simple demonstration of hindfoot flexibility in the cavovarus foot.

A simple prone examination for demonstrating both hindfoot flexibility and the "tripod" effect in the cavovarus foot has been implemented. This clinical evaluation can be performed without the use of any special equipment. Prone positioning also allows easy demonstration of deformity to family members.

Foot Deformities↗