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Biomedical subjects

A M Babey

Publications and source records attributed to A M Babey.

6 recordsLinked to original sources
PubMed1999

Altered adenylyl cyclase responsiveness subsequent to point mutations of Asp 128 in the third transmembrane domain of the delta-opioid receptor.

delta-Opioid receptors belong to the superfamily of G protein-coupled receptors, characterized by seven putative transmembrane domains, and have been shown to interact with a host of effector systems. It has been suggested that the charge on the conserved aspartic acid residue at position 128 in transmembrane domain 3 of the delta-opioid receptor contributes to both the conformation of the receptor binding pocket and the molecular rearrangements which accompany the establishment of high-affinity states of the receptor. In light of this, we used site-directed mutagenesis to determine whether this residue participates in the transmission of signals to adenylyl cyclase, the effector with which opioid receptors have been classically associated. Substitution of this aspartic acid (D128) for the neutral amino acid alanine, or the protonated amino acids lysine and histidine, constitutively couples the receptor to adenylyl cyclase, as evidenced by a curtailed response to forskolin stimulation in transfected cells. In addition, this constitutive activity can be blocked by pretreatment of the transfected cells with pertussis toxin. Interestingly, naloxone blocks this effect in cells expressing the D128A mutant, but acts as an agonist at the D128K mutant. Our findings support the hypothesis that the interaction between agonist and receptor promotes conformational changes that may be mimicked, at least in part, by mutation of the aspartate residue at position 128. Furthermore, these changes appear to be involved not only in receptor activation, but also in the functional discrimination between agonists and antagonists.

Adenylate Cyclase Toxin↗
PubMed1997

Functionally differentiating two neuronal nitric oxide synthase isoforms through antisense mapping: evidence for opposing NO actions on morphine analgesia and tolerance.

Several isoforms of neuronal nitric oxide synthase (nNOS) have been identified. Antisense approaches have been developed which can selectively down-regulate nNOS-1, which corresponds to the full-length nNOS originally cloned from the brain, and nNOS-2, a truncated form lacking two exons which is generated by alternative splicing, as demonstrated by decreases in mRNA levels. Antisense treatment also lowers nNOS enzymatic activity. Down-regulation of nNOS-1 prevents the development of morphine tolerance. Whereas morphine analgesia is lost in control and mismatch-treated mice given daily morphine injections for 5 days, mice treated with antisense probes targeting nNOS-1 show no decrease in their morphine sensitivity over the same time period. Conversely, an antisense probe selectively targeting nNOS-2 blocks morphine analgesia, shifting the morphine dose-response curve over 2-fold to the right. Both systems are active at the spinal and the supraspinal levels. An antisense targeting inducible NOS is inactive. Studies with NG-nitro-L-arginine, which does not distinguish among NOS isoforms, indicate that the facilitating nNOS-2 system predominates at the spinal level while the inhibitory nNOS-1 system is the major supraspinal nNOS system. Thus, antisense mapping distinguishes at the functional level two isoforms of nNOS with opposing actions on morphine actions. The ability to selectively down-regulate splice variants opens many areas in the study of nNOS and other proteins.

Analgesia↗
PubMed1995

Perspectives on the N-methyl-D-aspartate/nitric oxide cascade and opioid tolerance.

Opioid tolerance can be modulated by the N-methyl-D-aspartate/nitric oxide (NMDA/NO) cascade. Evidence exploring a daily injection paradigm indicates that agents antagonizing NMDA receptors can prevent tolerance to morphine and delta drugs, but not kappa agents. Drugs work regardless of whether they act as competitive or noncompetitive antagonists. Even an agent acting as an antagonist on the glycine site of the NMDA receptor is effective. Blockade of nitric oxide synthase has similar effects on opioid tolerance, preventing morphine and delta tolerance but not that of kappa drugs. Even methylene blue, which can inhibit guanylyl cyclase activity, is effective, presumably by blocking cGMP formation resulting from NO release. These results demonstrate the importance of an intact NMDA/NO cascade in the production of opioid tolerance and open new possibilities in the design of agents acting on opioid tolerance.

Animals↗
PubMed1994

Caffeine and propranolol block the increase in rat pineal melatonin production produced by stimulation of adenosine receptors.

The adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) injected i.p. during the light period increased rat pineal melatonin levels and this increase was blocked by simultaneous administration of the non-selective adenosine receptor antagonist caffeine. A single dose of the adenosine A1 agonist cyclopentyladenosine had no effect on nocturnal melatonin production. The NECA-stimulated increase was also blocked by the beta-adrenergic receptor antagonist propranolol. Given alone, neither caffeine nor propranolol had any effect on melatonin levels. The results point to an intermediate role for beta-adrenergic receptors in the adenosine-stimulated increase of melatonin production.

Adenosine↗
PubMed1994

Nitric oxide and opioid tolerance.

Under conditions in which NG-nitro-L-arginine (NOArg) treatment prevents morphine tolerance, NOArg induces a slow progressive inhibition of nitric oxide synthase (NOS), starting at approx. 20% after a single treatment and increasing to approx. 65% after 10 days. Studies designed to examine potential changes in NOS levels with chronic morphine administration reveal no change. Total NOS activity in both brainstem and cerebellum homogenates is unchanged, as are levels of NOS mRNA in a variety of brain regions. L-Arginine, the precursor of nitric oxide (NO), accelerates tolerance when coadministered with morphine and when given alone L-arginine decreases morphine's potency. Administration of L-arginine alone for 3-10 days shifts morphine's dose-response curve over 2-fold to the right while D-arginine is without effect, as is daily administration of L-arginine along with the NOS inhibitor NOArg. Thus, chronic L-arginine induces "tolerance" in opioid naive mice through NOS. Together, our data indicate an important role for NO in the modulation of opioid analgesia.

Amino Acid Oxidoreductases↗