Are developing β-adrenoceptors able to desensitize? Acute and chronic effects of β-agonists in neonatal heart and liver

2002 ◽  
Vol 283 (1) ◽  
pp. R205-R217 ◽  
Author(s):  
J. T. Auman ◽  
F. J. Seidler ◽  
C. A. Tate ◽  
T. A. Slotkin
Keyword(s):  
Cell Types ◽  
Adult Rats ◽  
Protein Activation ◽  
Heterologous Sensitization ◽  
G Protein Activation ◽  
Heterologous Desensitization ◽  
Ac Response ◽  
Β Adrenergic Receptors ◽  
Glucagon Receptors ◽  
Acute And Chronic Effects

During fetal and neonatal development, β-adrenergic receptors (β-ARs) appear to be resistant to desensitization by β-agonist drugs. To determine the mechanisms underlying the regulatory differences between adults and neonates, we administered isoproterenol, a mixed β1/β2-AR agonist, and terbutaline, a β2-selective agonist. Effects were examined in the ensuing 4 h after a single injection, or after the last of four daily injections. We prepared cell membranes from heart (predominantly β1-ARs) and liver (predominantly β2-ARs) and assessed signal transduction in the adenylyl cyclase (AC) pathway. In the first few hours after a single administration of isoproterenol to adult rats, cardiac β-ARs showed activation of G proteins (elevated AC response to forskolin) and desensitization of β-AR-mediated responses; after the fourth injection, heterologous desensitization emerged, characterized by a loss of signaling mediated either through β-ARs or glucagon receptors. Terbutaline evoked an increase in the forskolin response but no desensitization of receptor-mediated responses. When we gave the same treatments to neonatal rats, we observed cardiac G protein activation, but there was neither homologous nor heterologous desensitization of β-ARs or glucagon receptors. In the adult liver, isoproterenol and terbutaline both failed to evoke desensitization, regardless of whether the drugs were given once or for 4 days. In neonates, however, acute or chronic treatment elicited homologous desensitization of β-AR-mediated AC signaling, while sensitizing the response to glucagon. These results show that neonatal β-ARs are inherently capable of desensitization in some, but not all, cell types; cellular responses can be maintained through heterologous sensitization of signaling proteins downstream from the receptor. Differences from adult patterns of response are highly tissue selective and are likely to depend on ontogenetic differences in subtypes of β-ARs and AC.

Partial inhibition of SERCA is responsible for extracellular Ca2+ dependence of AlF–4-induced [Ca2+]i oscillations in rat pancreatic

2003 ◽  
Vol 285 (5) ◽  
pp. C1142-C1149 ◽  
Author(s):  
Seon Ah Chong ◽  
Soo Young Hong ◽  
Seok Jun Moon ◽  
Jee Won Park ◽  
Jeong-Hee Hong ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
G Proteins ◽  
Acinar Cells ◽  
Cell Types ◽  
Pancreatic Acinar Cells ◽  
Protein Activation ◽  
Partial Inhibition ◽  
G Protein Activation ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca

AlF4-is known to generate oscillations in intracellular Ca2+ concentration ([Ca2+]i) by activating G proteins in many cell types. However, in rat pancreatic acinar cells, AlF4--evoked [Ca2+]i oscillations were reported to be dependent on extracellular Ca2+, which contrasts with the [Ca2+]i oscillations induced by cholecystokinin (CCK). Therefore, we investigated the mechanisms by which AlF4- generates extracellular Ca2+-dependent [Ca2+]i oscillations in rat pancreatic acinar cells. AlF4--induced [Ca2+]i oscillations were stopped rapidly by the removal of extracellular Ca2+ and were abolished on the addition of 20 mM caffeine and 2 μM thapsigargin, indicating that Ca2+ influx plays a crucial role in maintenance of the oscillations and that an inositol 1,4,5-trisphosphate-sensitive Ca2+ store is also required. The amount of Ca2+ in the intracellular Ca2+ store was decreased as the AlF4--induced [Ca2+]i oscillations continued. Measurement of 45Ca2+ influx into isolated microsomes revealed that AlF4-directly inhibited sarco/endoplasmic reticulum Ca2+-ATPase (SERCA). The activity of plasma membrane Ca2+-ATPase during AlF4- stimulation was not significantly different from that during CCK stimulation. After partial inhibition of SERCA with 1 nM thapsigargin, 20 pM CCK-evoked [Ca2+]i oscillations were dependent on extracellular Ca2+. This study shows that AlF4- induces [Ca2+]i oscillations, probably by inositol 1,4,5-trisphosphate production via G protein activation but that these oscillations are strongly dependent on extracellular Ca2+ as a result of the partial inhibition of SERCA.

scholarly journals Direct Interactions with Gαi and Gβγ Mediate Nongenomic Signaling by Estrogen Receptor α

2007 ◽  
Vol 21 (6) ◽  
pp. 1370-1380 ◽  
Author(s):  
Premlata Kumar ◽  
Qian Wu ◽  
Ken L. Chambliss ◽  
Ivan S. Yuhanna ◽  
Susanne M. Mumby ◽  
...  
Keyword(s):  
Estrogen Receptor ◽  
G Protein ◽  
G Proteins ◽  
Cell Types ◽  
Estrogen Receptor Α ◽  
Erk Activation ◽  
Protein Activation ◽  
C Terminus ◽  
G Protein Activation ◽  
Oxide Synthase

Abstract Estrogen induces G protein-dependent nongenomic signaling in a variety of cell types via the activation of a plasma membrane-associated subpopulation of estrogen receptor α (ERα). Using pull-down experiments with purified recombinant proteins, we now demonstrate that ERα binds directly to Gαi and Gβγ. Mutagenesis and the addition of blocking peptide reveals that this occurs via amino acids 251–260 and 271–595 of ERα, respectively. Studies of ERα complexed with heterotrimeric G proteins further show that estradiol causes the release of both Gαi and Gβγ without stimulating GTP binding to Gαi. Moreover, in COS-7 cells, the disruption of ERα-Gαi interaction by deletion mutagenesis of ERα or expression of blocking peptide, as well as Gβγ sequestration with β-adrenergic receptor kinase C terminus, prevents nongenomic responses to estradiol including src and erk activation. In endothelial cells, the disruption of ERα-Gαi interaction prevents estradiol-induced nitric oxide synthase activation and the resulting attenuation of monocyte adhesion that contributes to estrogen-related cardiovascular protection. Thus, through direct interactions, ERα mediates a novel mechanism of G protein activation that provides greater diversity of function of both the steroid hormone receptor and G proteins.

scholarly journals RAMPs regulate signalling bias and internalisation of the GIPR

2021 ◽  
Author(s):  
Matthew Harris ◽  
Duncan I. Mackie ◽  
John B. Pawlak ◽  
Sabrina Carvalho ◽  
Tin T. Truong ◽  
...  
Keyword(s):  
G Protein ◽  
Gastric Inhibitory Polypeptide ◽  
General Role ◽  
Protein Activation ◽  
Glucose Levels ◽  
Blood Glucose Levels ◽  
G Protein Activation ◽  
Glucose Stimulated Insulin Secretion ◽  
Acute And Chronic Effects

AbstractGastric inhibitory polypeptide (GIP) receptor is a class B1 GPCR, that responds to GIP and physiologically potentiates glucose-stimulated insulin secretion. Like most class B1 GPCRs, GIPR has been shown to interact with RAMPs, yet the effects of RAMPs on its signalling and trafficking remain poorly understood. We demonstrate that RAMPs modulate G protein activation and GIPR internalisation profiles. RAMP3 reduced GIPR Gs activation and cAMP production but retained GIPR at the cell surface, and this was associated with prolonged ERK1/2 phosphorylation and β-arrestin association. By contrast, RAMP1/2 reduced Gq/11/15 activation of the GIPR. Through knockout mice studies, we show that RAMP1 is important to the normal physiological functioning of GIPR to regulate blood glucose levels. Thus, RAMPs act on G protein/β-arrestin complexes, having both acute and chronic effects on GIPR function, while this study also raises the possibility of a more general role of RAMP3 to enhance GPCR plasma membrane localisation.

scholarly journals The path from trigeminal asymmetry to cognitive impairment: a behavioral and molecular study

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Maria Paola Tramonti Fantozzi ◽  
Giulia Lazzarini ◽  
Vincenzo De Cicco ◽  
Angela Briganti ◽  
Serena Argento ◽  
...  
Keyword(s):  
Pupil Size ◽  
Muscle Spindles ◽  
Molecular Study ◽  
Contralateral Side ◽  
Acute Effects ◽  
Adult Rats ◽  
Afferent Inputs ◽  
Acute And Chronic Effects ◽  
The Brain ◽  
Mandibular Branch

AbstractTrigeminal input exerts acute and chronic effects on the brain, modulating cognitive functions. Here, new data from humans and animals suggest that these effects are caused by trigeminal influences on the Locus Coeruleus (LC). In humans subjects clenching with masseter asymmetric activity, occlusal correction improved cognition, alongside with reductions in pupil size and anisocoria, proxies of LC activity and asymmetry, respectively. Notably, reductions in pupil size at rest on the hypertonic side predicted cognitive improvements. In adult rats, a distal unilateral section of the trigeminal mandibular branch reduced, on the contralateral side, the expression of c-Fos (brainstem) and BDNF (brainstem, hippocampus, frontal cortex). This counterintuitive finding can be explained by the following model: teeth contact perception loss on the lesioned side results in an increased occlusal effort, which enhances afferent inputs from muscle spindles and posterior periodontal receptors, spared by the distal lesion. Such effort leads to a reduced engagement of the intact side, with a corresponding reduction in the afferent inputs to the LC and in c-Fos and BDNF gene expression. In conclusion, acute effects of malocclusion on performance seem mediated by the LC, which could also contribute to the chronic trophic dysfunction induced by loss of trigeminal input.

Opioid-Activated Postsynaptic, Inward Rectifying Potassium Currents in Whole Cell Recordings in Substantia Gelatinosa Neurons

1998 ◽  
Vol 80 (6) ◽  
pp. 2954-2962 ◽  
Author(s):  
S. P. Schneider ◽  
W. A. Eckert ◽  
A. R. Light
Keyword(s):  
Membrane Potential ◽  
G Protein ◽  
Potassium Currents ◽  
Substantia Gelatinosa ◽  
Opioid Agonist ◽  
Membrane Hyperpolarization ◽  
Whole Cell ◽  
Protein Activation ◽  
G Protein Activation ◽  
Whole Cell Recordings

Schneider, S. P., W. A. Eckert III, and A. R. Light. Opioid-activated postsynaptic, inward rectifying potassium currents in whole cell recordings in substantia gelatinosa neurons. J. Neurophysiol. 80: 2954–2962, 1998. Using tight-seal, whole cell recordings from isolated transverse slices of hamster and rat spinal cord, we investigated the effects of the μ-opioid agonist (d-Ala2, N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO) on the membrane potential and conductance of substantia gelatinosa (SG) neurons. We observed that bath application of 1–5 μM DAMGO caused a robust and repeatable hyperpolarization in membrane potential ( V m) and decrease in neuronal input resistance ( R N) in 60% (27/45) of hamster neurons and 39% (9/23) of rat neurons, but significantly only when ATP (2 mM) and guanosine 5′-triphosphate (GTP; 100 μM) were included in the patch pipette internal solution. An ED50 of 50 nM was observed for the hyperpolarization in rat SG neurons. Because G-protein mediation of opioid effects has been shown in other systems, we tested if the nucleotide requirement for opioid hyperpolarization in SG neurons was due to G-protein activation. GTP was replaced with the nonhydrolyzable GTP analogue guanosine-5′- O-(3-thiotriphosphate) (GTP-γ-S; 100 μM), which enabled DAMGO to activate a nonreversible membrane hyperpolarization. Further, intracellular application of guanosine-5′- O-(2-thiodiphosphate) (GDP-β-S; 500 μM), which blocks G-protein activation, abolished the effects of DAMGO. We conclude that spinal SG neurons are particularly susceptible to dialysis of GTP by whole cell recording techniques. Moreover, the depletion of GTP leads to the inactivation of G-proteins that mediate μ-opioid activation of an inward-rectifying, potassium conductance in these neurons. These results explain the discrepancy between the opioid-activated hyperpolarization in SG neurons observed in previous sharp electrode experiments and the more recent failures to observe these effects with whole cell patch techniques.

scholarly journals In vitro analysis of the origin and maintenance of O-2Aadult progenitor cells.

1992 ◽  
Vol 116 (1) ◽  
pp. 167-176 ◽  
Author(s):  
D Wren ◽  
G Wolswijk ◽  
M Noble
Keyword(s):  
Adult Life ◽  
Cell Types ◽  
Adult Rats ◽  
Optic Nerves ◽  
Limited Life ◽  
Old Rats ◽  
Vitro Analysis

We have been studying the differing characteristics of oligodendrocyte-type-2 astrocyte (O-2A) progenitors isolated from optic nerves of perinatal and adult rats. These two cell types display striking differences in their in vitro phenotypes. In addition, the O-2Aperinatal progenitor population appears to have a limited life-span in vivo, while O-2Aadult progenitors appear to be maintained throughout life. O-2Aperinatal progenitors seem to have largely disappeared from the optic nerve by 1 mo after birth, and are not detectable in cultures derived from optic nerves of adult rats. In contrast, O-2Aadult progenitors can first be isolated from optic nerves of 7-d-old rats and are still present in optic nerves of 1-yr-old rats. These observations raise two questions: (a) From what source do O-2Aadult progenitors originate; and (b) how is the O-2Aadult progenitor population maintained in the nerve throughout life? We now provide in vitro evidence indicating that O-2Aadult progenitors are derived directly from a subpopulation of O-2Aperinatal progenitors. We also provide evidence indicating that O-2Aadult progenitors are capable of prolonged self renewal in vitro. In addition, our data suggests that the in vitro generation of oligodendrocytes from O-2Aadult progenitors occurs primarily through asymmetric division and differentiation, in contrast with the self-extinguishing pattern of symmetric division and differentiation displayed by O-2Aperinatal progenitors in vitro. We suggest that O-2Aadult progenitors express at least some properties of stem cells and thus may be able to support the generation of both differentiated progeny cells as well as their own continued replenishment throughout adult life.

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