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Biomedical subjects

R D Green

Publications and source records attributed to R D Green.

At least 55 records · Page 3Linked to original sources
PubMed1988

Antidiabetic sulfonylureas control action potential properties in heart cells via high affinity receptors that are linked to ATP-dependent K+ channels.

Both avian and mammalian heart cells have high affinity receptors for antidiabetic sulfonylureas. The biochemical identification of these receptors has been carried out with [3H]glibenclamide. The Kd values for the most potent sulfonylureas, such as glibenclamide itself, are in the nanomolar range. Comparative studies of structure-function relationships indicate high similarities of binding properties between the sulfonylurea receptors in cardiac cells and insulinoma cells, respectively. The duration of the action potential of guinea pig cardiac cells was drastically reduced by decreasing intracellular ATP concentrations by perfusion or by blockade of oxidative phosphorylation. Glibenclamide was found to restore normal or nearly normal action potential properties in [ATP]in-depleted cardiac cells. Single channel recording using the patch-clamp technique has shown that this effect is associated with high affinity blockade of ATP-sensitive K+ channels by sulfonylureas.

ATP-Binding Cassette Transporters↗
PubMed1988

A low-priced computer-assisted densitometer and analysis software for quantitative autoradiography.

A computer-assisted densitometer which consists of a darkroom enlarger, a black-and-white exposure meter, an amplifier, an analog-to-digital converter, and a microcomputer with a monitor and a graphic printer can be utilized for the quantitative analysis of autoradiograms. QUANTAR, a computer program written in BASIC, records the density measurements and stores the data in a file that can be easily retrieved by commercially available spreadsheet software. A spreadsheet template was designed to convert the digital readings into concentration of ligand in tissue. A variety of spreadsheet templates can be created to analyze data for a standard curve, a Scatchard plot, or a binding competition curve. This system, which is easy to assemble, may be useful to the frugal investigator with a modest equipment budget.

Adenosine↗
PubMed1988

Adenosine A1 and A2 receptors of the substantia gelatinosa are located predominantly on intrinsic neurons: an autoradiography study.

Tissue autoradiography was used to examine the distribution of A1 and A2 adenosine receptors in the rat spinal cord. The distribution of binding sites for the A1 selective agonist, N6-[3H]-[(R)-1-methyl-2-phenylethyl]adenosine (R-[3H]PIA), was similar to the distribution of binding sites for [3H]-5'-N-ethylcarboxamide adenosine [( 3H]NECA), an agonist that binds to A1 and A2 receptors with nearly equal affinities. Binding site densities were highest in the substantia gelatinosa, followed by lamina 10; the remainder of the spinal cord displayed uniformly low levels of binding sites. In each of these three areas, [3H]NECA bound to more sites than R-[3H]PIA. When the A1-selective agonist, N6-(cyclopentyl)adenosine, was used to block [3H]NECA binding to A1 receptors, the autoradiograms demonstrated a band of A2 receptor density which tended to be localized in the ventral portion of the substantia gelatinosa. Unilateral dorsal rhizotomy, hemitransection and complete transection of the spinal cord failed to alter the [3H]NECA or R-[3H]PIA binding in the substantia gelatinosa. In contrast, unilateral microinjections of kainic acid into the dorsal horn decreased [3H]NECA and R-[3H]PIA binding at the level of the injections by 42 and 37%, respectively. In some areas, kainic acid injection eliminated all R-[3H]PIA and [3H]NECA binding in the substantia gelatinosa. It is therefore concluded that spinal cord A1 and A2 adenosine receptors in the substantia gelatinosa are located predominantly on intrinsic neurons.

Adenosine↗
PubMed1988

Characterization of cardiac A1 adenosine receptors by ligand binding and photoaffinity labeling.

[125I]N6-(p-aminobenzyl)adenosine and [125I]N6-(p-azidobenzyl)adenosine, which are potent agonists at A1 (Ri) adenosine receptors, have been used to characterize the adenosine receptor in membranes prepared from newborn chick heart. Scatchard analyses of [125I]N6-(p-aminobenzyl)adenosine binding to cardiac membranes revealed that the ligand bound to two affinity states of the receptor with Kd values of 0.7 and 9.9 nM. The corresponding maximum binding (Bmax) values were 25 and 86 fmol/mg of protein, respectively. In the presence of 0.1 mM 5'-guanylyl imidodiphosphate, a single affinity state was detected with a Kd of 9.4 nM and a Bmax of 96 fmol/mg of protein. Direct and indirect ligand binding studies with several adenosine receptor agonists and antagonists were used to compare the characteristics of the cardiac receptor with those of the A1 receptor in the cerebellum. The binding properties of the receptors in the two tissues were very similar although marked differences were observed in the binding kinetics of [125I]N6-(p-azidobenzyl)adenosine. Photo-affinity labeling experiments followed by sodium dodecyl sulfate-gel electrophoresis showed that the cardiac receptor had a apparent molecular weight of 37,600, which was slightly but significantly higher than that of the cerebellar receptor (35,500). The present results show that the cardiac receptor has ligand binding properties and a minimal subunit molecular weight similar to the more thoroughly studied A1 receptor in neural tissue.

Adenosine↗
PubMed1988

Desensitization of adenosine and dopamine receptors in rat brain after treatment with adenosine analogs.

Maximally tolerated doses of N6-[(R)-1-methyl-2-phenylethyl] adenosine (0.50 nmol/hr/2 wk), 5'-N-ethylcarboxamide adenosine (NECA, 0.04 nmol/hr/2 wk) or deoxycoformycin (5 nmol/hr/1 wk) were administered i.c.v. to rats using mini-osmotic pumps. Adenosine receptor function was subsequently assayed using both ligand binding and adenylate cyclase assays. Binding to A1 receptors was quantitated using [3H]N6-[(R)-1-methyl-2-phenylethyl]adenosine, a selective agonist ligand at A1 receptors. Differences in the binding of this ligand and that of [3H]NECA, which binds to A1 and A2 receptors with similar affinities, were used to quantitate A2 receptors. None of the treatments affected A1 receptor function as assessed by both ligand binding and adenylate cyclase assays. A2 receptor binding and A2 receptor-mediated stimulation of adenylate cyclase were blunted in striatal membranes from NECA- and deoxycoformycin-treated rats but unaffected in striatal membranes from N6-[(R]-1-methyl-2-phenylethyl]adenosine-treated rats. All three pretreatments attenuated D1 dopamine receptor-mediated stimulation of adenylate cyclase in striatal membranes. These results suggest that 1) the A2 adenosine receptor system is susceptible to desensitization and 2) different mechanisms are involved in the NECA- and deoxycoformycin-induced desensitization of A2 adenosine receptor and D1 dopamine receptor systems. It is suggested that the D1 dopamine receptor desensitization is, in fact, due to the tonic stimulation of adenosine A1 receptors.

Adenosine↗
PubMed1987

Correlation of agonist-induced phosphorylation of chick heart muscarinic receptors with receptor desensitization.

We have determined whether the process of agonist-mediated phosphorylation of the muscarinic receptor correlates with the process of muscarinic receptor desensitization in chick cardiac tissue. Exposure of ventricular slices to the agonist carbachol under conditions previously shown to lead to large increases in muscarinic receptor phosphorylation (Kwatra, M. M., and Hosey, M. M. (1986) J. Biol. Chem. 261, 12429-12432) resulted in decreased affinity of the muscarinic receptor for agonists. The agonist oxotremorine mimicked and the antagonist atropine prevented the effects of carbachol on receptor phosphorylation and agonist affinity. The time courses and concentration dependences for agonists to induce phosphorylation of the muscarinic receptor and decreases in agonist affinity were similar. Treatment of chick atria with acetylcholine under conditions which led to receptor phosphorylation resulted in decreased sensitivity of these preparations to the negative inotropic effect of carbachol. Taken together, the results support the concept that phosphorylation of cardiac muscarinic receptors may be related to the process of receptor desensitization. The mechanism by which agonists induce receptor phosphorylation was also investigated. The phosphorylated amino acids formed in response to agonists were serine and threonine. The protein kinase C activator phorbol myristate acetate had no effect on receptor phosphorylation or agonist affinity, nor did it prevent the effects of carbachol on either of these parameters. Receptor phosphorylation also was unaffected by the calmodulin antagonists W-7 and W-13, by elevation of cyclic nucleotides, and by agonists which activate other cardiac receptor systems. The results suggest that the phosphorylation of cardiac muscarinic receptors requires agonist occupancy of the receptor and/or may involve the participation of a selective protein kinase.

Animals↗
PubMed1987

N6-phenyladenosines: pronounced effect of phenyl substituents on affinity for A2 adenosine receptors.

A number of N6-phenyladenosines with various substitutions on the phenyl ring have been synthesized and tested for their affinities toward brain A1 and A2 adenosine receptors. Compounds with meta substituents, such as (m-hydroxy- and m-iodophenyl)adenosine, were found to have high A1 selectivity. Meta substitution caused a selective decrease in the affinity of these compounds for A2 receptors. The results suggest that, in contrast to what is commonly held, certain N6-substituents have pronounced effects on affinity for brain A2 adenosine receptors. Thus, brain A2 receptors may have a well-defined region that recognizes N6-substitutions.

Adenosine↗
PubMed1987

Twenty years of treating decompression sickness.

Twenty years of treatment records were searched for cases of serious decompression sickness (DCS). Spinal cord DCS was the most common presentation. The efficacy of various treatment tables were compared. Oxygen tables were found to be as effective as long air tables in treating cases presenting within 12 h of the onset of symptoms and were superior for cases presenting later. Using RN 61 (USN 5) to treat serious decompression sickness resulted in a high post-treatment relapse rate. Other inappropriate practices such as in-water air treatment and nontreatment of spontaneously recovering cases resulted in a high incidence of deterioration or relapse.

Air↗
PubMed1987

Identification of A1 and A2 adenosine receptors in the rat spinal cord.

The adenosine receptors in membranes prepared from rat ventral and dorsal lumbar spinal cord were characterized by comparing the binding characteristics of [3H]5'-N-ethylcarboxamide adenosine ([3H]NECA), an agonist with nearly equal affinities at the A1 and A2 adenosine receptor subtypes, with those of [3H]N6-[(R)-1-methyl-2-phenylethyl]adenosine ([3H]R-PIA), an A1-selective agonist. Saturation isotherms of the ventral and dorsal spinal cord yielded Kd values 1.9 to 2.3 nM for [3H]R-PIA and 18.1 to 19.5 nM for [3H]NECA. The Bmax for [3H]NeCA was approximately twice the Bmax for [3H]R-PIA in ventral and dorsal halves (267 vs. 128 fmol/mg of protein and 402 vs. 206 fmol/mg of protein, respectively). Displacement of specific [3H]NECA binding by the A2-selective agonist, 2-(phenylamino)adenosine, the relatively nonselective antagonist, theophylline and six A1-selective agonists, R-PIA, S-PIA, N6-(cyclohexyl)adenosine, N6-(cyclopentyl)adenosine, N6-(m-aminophenyl)adenosine and N6-(m-iodophenyl)adenosine, revealed two [3H]NECA binding components with the characteristics of A1 and A2 receptors. All curves best fit a two-site model when analyzed by the computer program LIGAND. R-PIA, N6-(cyclohexyl)adenosine and N6-(cyclopentyl)adenosine were the most potent displacers at the first site (Ki = 0.6-1.4 nM). All A1-selective agonists were poor displacers of [3H]NECA at the second site (Ki = 0.6-18.6 microM). The A2-selective agonist, 2-(phenylamino)adenosine, was as potent as R-PIA in displacing [3H]NECA from this site with a Ki value 0.57 microM. Finally, the A1 and A2 adenosine receptor-mediated inhibition and stimulation of adenylate cyclase were demonstrated directly in synaptic membranes prepared from the spinal cord.

Adenosine↗
PubMed1986

The activity of the Na+/H+ antiporter in cultured cardiac cells is dependent on the culture conditions used.

When chick cardiac cells are maintained in serum-free NCTC-135 medium, the pHi dependence of the Na+/H+ exchanger is much more acidic (pK = 7.0) than when a serum-free M199 medium is used (pK greater than 7.5). Phorbol esters activate the Na+/H+ exchanger and produce a cell alkalinization in cells maintained in NCTC-135 medium by shifting the pHi dependence of the system to more alkaline values. They have no action on cells maintained in M199 medium. The alkaline pHi dependence of the Na+/H+ exchanger and the loss of responsiveness of phorbol ester action in M199 medium correlate with increased rates of phosphatidylinositol turnover.

Amiloride↗
PubMed1986

The Na+/H+ antiport of eukaryotic cells: relationship between the kinetic properties of the system and its physiological function.

The Na+/H+ antiport is present in the plasma membrane of virtually all vertebrate cells and it plays a central role in cell homeostasis. The pharmacological properties and the characteristics of the interaction of extracellular Na+, Li+, H+ and of intracellular H+ with the Na+/H+ antiport are reviewed herein. The kinetic properties of the system are shown to be essential for defining its four main physiological functions: transepithelial ion transport, control of the pHi, control of the intracellular Na+ concentration, and control of the cell volume. The activity of the Na+/H+ antiport can be modulated by a large number of effectors which are thought to act via protein kinases. At least three mechanisms of activation of the Na+/H+ exchanger are defined from the analysis of the kinetic properties of the system. Activation of the Na+/H+ antiport leads to very different consequences, depending upon the activity of other ion transporting systems in the membrane.

Animals↗
PubMed1986

Pulmonary barotrauma in divers and the treatment of cerebral arterial gas embolism.

A review of case records spanning 20 years revealed 140 cases of decompression pulmonary barotrauma (PBT) in divers. There were 23 cases of uncomplicated PBT and 117 cases of cerebral arterial gas embolism (AGE), of which 58 had respiratory manifestations. Details of presentation and precipitating factors were analysed. Half of AGE cases improved spontaneously, including 21% which recovered completely. The 89 treated cases of AGE (including 2 iatrogenic cases) were used to study the efficacy of different treatments. An overall success rate of 65% was seen with 62% of cures occurring within 25 min of arrival at pressure. The remaining cures occurred in equal numbers during decompression and after surfacing. No cases receiving steroids relapsed. Increasing the time to treatment reduced the likelihood of cure. Comparison of treatments proved difficult and it was concluded that, although most cases would probably respond satisfactorily to 2.8 bar (2100 mm Hg) of oxygen, there were no compelling reasons for altering the current treatment practice of beginning treatment of acute cases with a 30-min period at 6.0 bar (165 fsw) before returning to 2.8 bar (60 fsw) to complete the therapy.

Barotrauma↗
PubMed1986

Recurrent pulmonary barotrauma.

Twenty years of diving incident records were searched to find the 12 cases of recurrent pulmonary barotrauma (PBT) reported. The trend observed was that recurrences tended to be worse than the first incident and more likely to include arterial gas embolism (AGE). It is concluded that the Royal Navy policy of preventing all divers who suffer PBT from further diving is justified, regardless of the cause or mild nature of the injury. The incidence of AGE was low at 1 per 19,800 to 1 per 34,000 dives and was similar to United States Navy incidence. There was no evidence that routine screening by simple spirometry had influenced the PBT rate and, therefore, its usefulness is questioned.

Adult↗
PubMed1986

Pulmonary barotrauma in submarine escape trainees and the treatment of cerebral arterial air embolism.

The reports of all dysbaric incidents occurring during submarine escape training at the Royal Navy's training facility in HMS Dolphin during 1954-84 were reviewed. All cases treated for unequivocal arterial gas embolism were used to assess the effectiveness of various treatments. Presentation and accident rates were analysed. As training techniques and treatments have varied over the years, the data were not uniform thus making comparison of treatments difficult. Both long air tables and RN Table 63 (USN6A) appear to offer effective treatment. There was insufficient data to assess the efficacy of prophylactic steroids in preventing relapse. It was concluded that the current recommendations for treating AGE by commencing on RN Table 63 with a change to RN Table 54 in the event of no response or of relapse should remain unchanged.

Accident Prevention↗
PubMed1985

Specific photoaffinity labelling of inhibitory adenosine receptors.

N6(L-phenylisopropyl)adenosine (L-PIA) and N6(3-iodo-4-azido benzyl)-adenosine (IAzBA) inhibit the adenylate cyclase activity in synaptic membranes of chick cerebellum via Ri adenosine receptors. [3H]L-PIA and [125I]AzBA bind to these membranes with Kd values of approximately 1 nM and Bmax values of approximately 1000 fmol/mg protein. Photolysis of [125I]AzBA bound to synaptic membranes results in the specific incorporation of radioactivity into a protein with Mr = 36,000. This photoincorporation is blocked by simultaneous exposure to L-PIA, theophylline, an adenosine receptor antagonist, or Gpp(NH)p, but not by cytosine, suggesting that the 36,000 dalton protein is the Ri adenosine receptor or a subunit of the receptor that contains the adenosine binding site.

Adenosine↗
PubMed1985

Attenuation of chick heart adenylate cyclase by muscarinic receptors after pertussis toxin treatment.

Pertussis toxin selectively modifies the function of Ni, the inhibitory guanine nucleotide binding protein of the adenylate cyclase complex. In chick heart membranes, guanine nucleotide activation of Ni resulted in a decrease in the apparent affinity of the muscarinic receptor for the agonist oxotremorine, inhibition of basal adenylate cyclase activity, and the attenuation of adenylate cyclase by oxotremorine. Treatment of chicks with pertussis toxin caused the covalent modification of 80-85% of cardiac Ni. After this treatment Gpp(NH)p had no effect on muscarinic receptor affinity and GTP stimulated basal adenylate cyclase activity. In contrast, the GTP-dependent attenuation of adenylate cyclase caused by muscarinic receptors was unaffected.

Adenosine Diphosphate Ribose↗