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R J Miller

Publications and source records attributed to R J Miller.

At least 325 records · Page 18Linked to original sources
PubMed1984

Calcium channel activation: a different type of drug action.

Depolarization of NG108-15 (neuroblastoma-glioma) cells causes an increase in 45Ca2+ influx. This effect is blocked by low concentrations of dihydropyridines such as nitrendipine and by other blockers of voltage-sensitive calcium channels such as D-600, diltiazem, and Cd2+. Two other dihydropyridines, BAY K8644 and CGP 28392, have the opposite effect. Low concentrations of these compounds enhance depolarization-induced 45Ca2+ influxes. BAY K8644 is more effective than CGP 28392. Both agents have no effect on fluxes measured under nondepolarizing conditions. The effects of BAY K8644 and CGP 28392 can be inhibited by nitrendipine, D-600, diltiazem, or Cd2+. Whereas the interaction between nitrendipine and BAY K8644 is shown to be competitive in nature, that between BAY K8644 and D-600 is shown to be noncompetitive. These results indicate that dihydropyridines show a variety of effects on calcium channels, ranging from agonistic through partially agonistic to antagonistic. Moreover, the results also indicate that dihydropyridines and D-600 exert their effects on calcium channels at different sites.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1984

Identification and characterization of voltage-sensitive calcium channels in neuronal clonal cell lines.

Voltage-sensitive calcium channels ( VSCCs ) have been identified in three clonal cells. These are the neuroblastoma X Chinese hamster brain hybrid ( NCB -20), the neuroblastoma X glioma hybrid (NG108-15), and the neuroblastoma ( N4TG1 ). Depolarization of NCB -20 cells with 50 mM KCl or 50 microM veratridine (VE) produced a 2- to 3-fold increase in net 45Ca2+ uptake. In NCB -20 cells, this voltage-sensitive 45Ca2+ uptake was inhibited selectively by organic calcium antagonists such as nitrendipine, cinnarizine, verapamil, and diltiazem (IC50 values = 6.4, 750, 1800, and 4500 nM, respectively). High K+-induced uptake was unaffected by 4-aminopyridine, tetraethylammonium, and tetrodotoxin (TTX), whereas VE-induced 45Ca2+ uptake was completely blocked by 3 microM TTX. In contrast to NCB -20 cells, NG108-15 cells showed a much smaller response to depolarizing stimuli. Following differentiation of NG108-15 cells by chronic treatment with 10 microM prostaglandin E1 and 50 microM 3-isobutyl-1-methylxanthine, depolarization induced a large increase in voltage-sensitive 45Ca2+ uptake. This induction was apparent after 24 hr and increased linearly for 96 hr. VSCC activity was also induced by 1.5% dimethyl sulfoxide and by other agents that increase intracellular cAMP, such as forskolin (1 microM) and cholera toxin (1 microgram/ml). Voltage-sensitive 45Ca2+ uptake in differentiated NG108-15 cells was inhibited by nitrendipine, D-600, and diltiazem (IC50 values = 7, 690, and 1600 nM). Our results suggest that VSCCs in neuronal clonal cell lines can be altered by cellular differentiation. In contrast to those VSCCs involved in neurotransmitter release, the VSCCs described here appear to be blocked by organic calcium channel antagonists at very low concentrations.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Adrenergic mediation of the intestinal antisecretory action of opiates administered into the central nervous system.

The antisecretory effects of the stable enkephalin analogs, [D-Ala2-Met5] enkephalinamide (DAMA) and [D-Ala2-D-Leu5] enkephalin, and the opiate drug morphine were evaluated on fluid secretion induced by cholera toxin in isolated loops of the jejunum and proximal and distal ileum in anesthetized rats. Intracerebroventricular administration of DAMA (0.03-3 micrograms) or [D-Ala2-D-Leu5] enkephalin (1.0-10 micrograms) dose-dependently reduced secretion in the jejunum without affecting fluid movement in the other small intestinal segments. Morphine in doses up to 30 micrograms i.c.v. had no significant antisecretory effects. Intravenous administration of DAMA, at doses up to 3000 micrograms/kg, had little effect on intestinal fluid accumulation. The antisecretory action of DAMA (3 micrograms i.c.v.) was completely blocked by pretreatment with the alpha adrenergic antagonist phentolamine and after peripheral sympathectomy induced by guanethidine. In contrast, DAMA activity was preserved in adrenal demedullated rats. DAMA had no significant effects upon mean arterial blood pressure or on blood acid-base balance. These results suggest that the antisecretory effects of opiates are, at least partly, mediated at sites within the central nervous system. These actions are probably a consequence of increased activity in sympathetic nerve fibers innervating the upper small intestine.

Animals↗
PubMed1984

An antiabsorptive basis for precipitated withdrawal diarrhea in morphine-dependent rats.

Diarrhea is a common manifestation of withdrawal from opiates in dependent subjects. This study examined the possibility that this diarrhea results in part from alterations in intestinal fluid transport. Isolated loops of jejunum, ileum and colon were created in morphine-dependent and nondependent rats implanted s.c. with morphine or lactose pellets, respectively. The administration of naltrexone (1 mg/kg s.c.) or its quaternary analog methylnaltrexone (0.01-3 mg/kg i.v.), which does not readily cross the blood-brain barrier, produced a dose-related reduction in fluid absorption from the jejunum and colon of dependent animals only. Similar effects were observed after the i.c.v. injection of quaternary naltrexone (1.0-10 microgram/rat). Both narcotic antagonists, given by any route, produced no change in ileal absorption. Pretreatment with hexamethonium (10 mg/kg i.v.) or atropine (4 mg/kg i.v.) attenuated the antiabsorptive effects of quaternary naltrexone on the jejunum. Serosal addition of naltrexone (10 microM) had no effect on Na or Cl fluxes, short-circuit current or tissue conductance across isolated segments of intestinal mucosa from dependent and nondependent rats. These results indicate that precipitated opiate withdrawal is associated with decreases in jejunal and colonic fluid absorption mediated at sites within both the central nervous system and periphery. Moreover, these effects are not a consequence of a direct opiate action on enterocytes.

Animals↗
PubMed1984

Overaccommodation, underaccommodation, and the clinical phoropter: a study of instrument myopia and related effects.

To explore the degree to which a phoropter can induce overaccommodation (instrument myopia) and/or underaccommodation , 19 college-age subjects participated in a series of measurements of accommodation response. Accommodation responses were assessed while subjects looked through a phoropter (both with standard 19-mm viewing apertures and through 2-mm artificial pupils) and when no phoropter was present. Subjects were tested both monocularly and binocularly, and under three stimulus conditions (near target, far target, and total darkness). Even without the phoropter , subjects tended to overaccommodate for the far target. The 19-mm phoropter produced no significant overaccommodation or underaccommodation effects over and above those observed without the presence of the phoropter . The 2-mm artificial pupils produced significantly more underaccommodation for the near target. Results indicate a tendency for accommodation response to approach an intermediate resting position as the viewing situation becomes impoverished.

Accommodation, Ocular↗
PubMed1983

Chronic opiate treatment does not modify alpha 2-adrenergic receptors in rat cerebral cortex, kidney and in the neurotumor cell line NCB20.

We examined the effect of chronic opiate treatment on the alpha 2-adrenergic receptor binding of both the agonist [3H]clonidine and the antagonist [3H]yohimbine in the cerebral cortex and kidney of rats. In addition, we demonstrated the presence of an adrenergic receptor of the alpha 2 type on the neurotumor cell line NCB20 and used this cell line as a model for studying the interaction between the opiate and alpha 2-adrenergic systems. In all the three above systems, chronic opiate treatment did not modify the number or the affinity of alpha 2-adrenergic receptors.

Animals↗
PubMed1983

Inhibition of the antisecretory effects of [D-Ala2,D-Leu5]enkephalin in the guinea-pig ileum by a selective delta opioid antagonist.

The novel opioid antagonist [diallyl-Tyr1,(CH2)S-Phe4,Leu5]enkephalin (M154,129) was examined for its ability to block the antisecretory effects of [D-Ala2,D-Leu5]enkephalin (DADLE) in isolated mucosal segments of the guinea-pig ileum, actions mediated predominantly through the delta opiate receptor. DADLE reduced transepithelial potential difference and short-circuit current (ED50 18 nM); these effects were competitively antagonized by M154,129 with a Ke value of 746 nM. These results are consistent with others demonstrating M154,129 is a relatively selective although not highly potent blocker of delta opiate receptors.

Animals↗
PubMed1983

Examination of the requirement for an amphiphilic helical structure in beta-endorphin through the design, synthesis, and study of model peptides.

In our approach to beta-endorphin modeling, we have proposed that the biological properties of the natural peptide are determined by the combination of three basic structural units: a highly specific opiate recognition sequence at the NH2 terminus (residues 1-5) connected via a hydrophilic peptide link (residues 6-12) to a potential amphiphilic helix in the COOH-terminal residues 13-31. In the alpha-helical conformation the hydrophobic domain twists around the length of the helix and covers almost one-half of its surface. The other distinctive features of the helix include its basicity and the two aromatic residues Phe18 and Tyr27. In contrast to previous models we have studied, peptide 4 is a "negative" model in the sense that it was designed and examined in order to determine how the lack of a well defined amphiphilic structure affects the biological properties of beta-endorphin. For this purpose, peptide 4 retains the three structural units previously postulated for beta-endorphin, but the amino acids of the 13-31 region are arranged in such a way that no definite continuous hydrophobic zone could be formed in an alpha- or pi-helical conformation of this region. In aqueous buffered solutions, peptide 4 showed almost the same amount of alpha-helical structure as beta-endorphin, with a slight tendency toward less helicity in 50% aqueous 2,2,2-trifluoroethanol. In rat brain homogenate, peptide 4 was degraded slightly slower than beta-endorphin, in contrast to the apparently much higher stability of previous models under the same conditions. With regard to opiate receptor binding, peptide 4 was twice as potent as beta-endorphin in mu-receptor assays but half as potent in delta-receptor assays. The opiate potency of peptide 4 on the guinea pig ileum was higher than that of beta-endorphin. In contrast, in the rat vas deferens assay, which is very specific for beta-endorphin, the potency of peptide 4 was very low and could be shown not to be mediated by the same opiate mechanism or by the same opiate receptor. A comparison of these results with those of previous model peptides provides further evidence for the importance of an amphiphilic helical structure in beta-endorphin residues 13-31, which determines the resistance to proteolysis of the natural molecule and contributes to the delta- and mu-opiate receptor interaction. The amphiphilicity of this helical structure must also be essential for high opiate activity on the rat vas deferens (epsilon-receptors), whereas no such structural requirement appears to be necessary for interaction with the opiate receptors on the guinea pig ileum.

Amino Acid Sequence↗
PubMed1983

CNS involvement in the antisecretory action of [Met5]enkephalinamide on the rat intestine.

The effects of the stable enkephalin, [D-Ala2, Met5]enkephalinamide (DAMA) were examined on basal and stimulated fluid accumulation in intestinal loops of anesthetized Wistar-Furth rats. DAMA (0.1-3.0 micrograms, i.c.v.) dose-dependently increased basal fluid absorption in the medial ileum and decreased jejunal and proximal ileal fluid secretion after 4 h cholera toxin (1 microgram/loop) pretreatment. The antisecretory effects of DAMA were blocked by naltrexone (1 mg/kg s.c.). Thus, the antisecretory effects of opioids may be partially mediated at CNS sites.

Animals↗
PubMed1983

The direct effect of insulin on canalicular bile flow.

Previous experimental studies in dogs have demonstrated the choleretic effects of insulin administered in physiologic doses. In our experiment the isolated perfused rat liver was used as an in situ model for demonstrating the direct effects of insulin on bile salt independent canalicular bile flow. Livers were initially perfused with oxygenated Krebs-Ringer buffer solution of 20% hematocrit after which sodium taurocholate (18.3 mg hr-1) was infused to stabilize bile flow. Insulin (0.5 unit kg-1 hr-1) or saline was then given for a 90-min test period. Control (C) and experimental (E) rats were perfused simulataneously (n = 11). Bile flow was significantly greater in the experimental (21.76 +/- 2.16 microliters g liver-1 15 min-1) than the control (16.87 +/- 2.08 microliters g liver-1 15 min-1) group (P less than .01). In addition, the percentage change in flow in individual rats from baseline values was significantly different with peak effect occurring 45 min after start of hormone infusion (E = +19 +/- 3%, C = -5 +/- 7%) (P less than 0.003). Bile analysis revealed stable bile salt concentrations (E = 7.41 +/- .25, C = 7.8 +/- .24 mM ml-1) and stable bile salt outputs (E = 1.68 +/- .14, C = 1.33 +/- .13 mM 15 min-1) for both groups. Biliary cholesterol outputs did not differ between groups (E = 42.6 +/- 4.8, C = 38.2 +/- 7.4 micrograms 15 min-1), nor did phospholipid outputs (E = 3.56 +/- .63, C = 2.71 +/- .57 mg 15 min-1). These data support the hypothesis that the choleretic action of insulin is a direct one on the hepatocyte, requiring no intermediate step or mediator.

Animals↗
PubMed1983

Distribution and projections of nerves with enkephalin-like immunoreactivity in the guinea-pig small intestine.

Whole mounts of guinea-pig small intestine were used to examine the distribution of neurons with enkephalin-like immunoreactivity and the effects of microsurgical lesions on these neurons. The enkephalin neurons are intrinsic to the intestine. Cell bodies are found in the myenteric ganglia; processes are in the myenteric plexus, circular muscle (including deep muscular plexus) and submucosa, but not in the mucosa. The cell bodies have one prominent process and several short processes, the latter occasionally are seen to give rise in turn to fine, faint processes. The prominent processes provide fibres to the circular muscle and deep muscular plexus beneath and just anal (up to about 2 mm) to the cell bodies. Fibres in the submucous ganglia come from the overlying myenteric plexus. Orally-directed processes (possibly dendrites) of myenteric cell bodies provide the varicose fibres in the myenteric ganglia. These processes are 3.5-4 mm long. The enkephalin neurons represent a population of enteric neurons, with a distinct distribution and projections, which does not correspond to any of the other populations of enteric neurons that have been studied.

Animals↗
PubMed1983

Use of a ready signal in accommodation assessment.

The usual procedure in making laser optometer measurements of accommodation is to precede each trial with a ready signal. Given previous findings that stress, arousal, attention, etc., can influence accommodation and related phenomena, the question arises as to whether such a ready signal might induce some form of orientation response reflected in alterations of accommodation. Dark focus (DF) accommodation (accommodation in total darkness) was assessed in 26 young adults (13 males and 13 females) under two conditions, one of which involved the use of a ready signal and the other did not. Analyses showed that the presence or absence of the ready signal had no differential impact on accommodation.

Accommodation, Ocular↗
PubMed1983

Enterocyte alpha 2-adrenergic receptors: yohimbine and p-aminoclonidine binding relative to ion transport.

We previously reported that alpha 2-adrenergic agonists enhance absorption and inhibit secretion of electrolytes in small intestine. The present study was undertaken to characterize and localize the relevant receptors. Plasma membranes derived from isolated rabbit ileal epithelial cells were incubated with either [3H]yohimbine (Yo), an alpha 2-antagonist, or p-[3H]aminoclonidine (PAC), an alpha 2-agonist. Scatchard analysis of [3H]Yo binding suggests a single receptor. Competitive displacement of Yo from this receptor by other ligands had a potency order characteristic for alpha 2-receptors in other tissue systems. A Scatchard plot of [3H]PAC binding was curvilinear and best fit by assuming two independent site. Competitive displacement of [3H]PAC by PAC in the presence of 140 mM Na+ or 0.1 mM GTP increased the IC50 for PAC binding from 10 nM to 100 and 105 nM, respectively, and the Hill coefficient from 0.7 to 1.2 and 1.0, respectively. The ED50 for PAC effect on short-circuit current (200 nM) does not differ significantly from these values. We conclude that alpha 2-receptors are present on ileal enterocytes and that these receptors mediate enterocyte fluid and electrolyte transport function.

Animals↗
PubMed1983

Bradykinin-stimulated electrolyte secretion in rabbit and guinea pig intestine. Involvement of arachidonic acid metabolites.

Bradykinin (BK) increases short-circuit current (Isc) when added to the serosal side of rabbit or guinea pig ileum or rabbit colon. Significant effects on Isc are seen at concentrations as low as 10(-10) M. Anion substitution experiments and unidirectional 36Cl flux measurements indicate that this effect of BK on Isc is due to Cl secretion. The effect of BK on Isc can be partially blocked (60-70% inhibition) by cyclooxygenase inhibitors (indomethacin and/or naproxen) and completely blocked by the phospholipase inhibitor, mepacrine. The combined cyclooxygenase/lipoxygenase inhibitors BW 755 and eicosa-5,8,11,14-tetraynoic acid (ETYA) also completely block the effect of BK on Isc but the slow-reacting substance of anaphylaxis (SRS-A) antagonist FPL 55712 has no effect. None of the above inhibitors diminish the effect on Isc of other exogenously added secretory stimuli such as vasoactive intestinal peptide (VIP), theophylline, or prostaglandin E2 (PGE2). Prior desensitization of rabbit ileum to PGE2 blocks the effect on Isc of BK but not those of VIP or theophylline. Conversely, prior desensitization of rabbit ileum to BK greatly reduces the effect of PGE2 on Isc. BK also stimulates the synthesis of PGE2 in rabbit ileal and colonic mucosa and this effect can be blocked by prior addition of either indomethacin or mepacrine. These effects of BK are similar to those of exogenously added arachidonic acid (AA). AA also stimulates Cl secretion and increases PGE2 synthesis and its effect on Isc can be inhibited by prior desensitization to PGE2 or by prior addition of indomethacin. The above results indicate that BK stimulates active Cl secretion in both small and large intestine and suggest that this effect is due to the intracellular release of AA. Although the prostaglandins appear to be the major products of AA metabolism contributing to the secretory response, lipoxygenase products may also play a role.

Animals↗