cyclic AMP

There are two families of dopamine (DA) receptors, called D1 and D2, respectively. The D1 family consists of D1- and D5-receptor subtypes and the D2 family consists of D2-, D3-, and D4-receptor subtypes. The amino acid sequences of these receptors show that they all belong to a large superfamily of receptors with seven transmembrane domains, which are coupled to their

Relaxin is one of the 6-kDa peptide hormones, which acts as a pleiotropic endocrine and paracrine factor. Our previous studies revealed that sperm capacitating medium containing relaxin induced capacitation and acrosome reaction (AR) in fresh and frozen-thawed porcine or bovine spermatozoa. However, the intracellular signaling cascades involved with capacitation or AR induced by relaxin was unknown. Therefore, the present study was designed to investigate the intracellular signaling cascades involved with capacitation and AR induced by relaxin in fresh and frozen-thawed bovine spermatozoa. Spermatozoa were incubated in sperm Tyrode's albumin lactate pyruvate (Sp-TALP) medium supplemented with (40 ng ml(-1)) or without relaxin, and subjected to evaluation of chlortetracycline staining pattern, cholesterol efflux, Ca(2+)-influx, intracellular cyclic adenosine monophosphate (cAMP) and protein tyrosine phosphorylation. Capacitation and AR were increased (P<0.05) in both fresh and frozen-thawed spermatozoa incubated with relaxin. Cholesterol effluxes were greater in the fresh (P<0.01) and frozen-thawed (P<0.05) spermatozoa incubated with relaxin than the spermatozoa incubated without relaxin. Ca(2+)-influxes were also significantly stimulated by relaxin in the fresh (P<0.01) and frozen-thawed (P<0.05) spermatozoa. The Sp-TALP medium containing relaxin influenced the generation of intracellular cAMP in the fresh (P<0.01) and frozen-thawed (P<0.05) spermatozoa, and exhibited higher exposure of protein tyrosine phosphorylation in both sperm types than the medium devoid of relaxin. Therefore, the results postulate that relaxin exerts the intracellular signaling cascades involved with capacitation and AR through accelerating the cholesterol efflux, Ca(2+)-influx, intracellular cAMP and protein tyrosine phosphorylation in fresh and frozen-thawed bovine spermatozoa.

Neurofibromatosis type I (Nf1) is a GTPase-activating protein (GAP) that inactivates the oncoprotein Ras and plays important roles in nervous system development and learning. Alternative exon 23a falls within the Nf1 GAP domain coding sequence and is tightly regulated in favor of skipping in neurons; however, its biological function is not fully understood. Here we generated mouse embryonic stem (ES) cells with a constitutive endogenous Nf1 exon 23a inclusion, termed Nf1 23aIN/23aIN cells, by mutating the splicing signals surrounding the exon to better match consensus sequences. We also made Nf1 23aΔ/23aΔ cells lacking the exon. Active Ras levels are high in wild-type (WT) and Nf1 23aIN/23aIN ES cells, where the Nf1 exon 23a inclusion level is high, and low in Nf1 23aΔ/23aΔ cells. Upon neuronal differentiation, active Ras levels are high in Nf1 23aIN/23aIN cells, where the exon inclusion level remains high, but Ras activation is low in the other two genotypes, where the exon is skip...

Prostacyclin (PGI 2 ) possesses various physiological functions, including modulation of nociception, inflammation and cardiovascular activity. Elucidation of these functions has been hampered by the absence of selective IP receptor antagonists. ... Two structurally distinct ...

Active calcium transport by cardiac sarcoplasmic reticulum assumes a central role in the excitation-concentration coupling of the myocardium, in that Ca2+-dependent ATPase (mol.wt. 100 000) of cardiac sarcoplasmic reticulum serves as an energy transducer and a translocator of Ca2+ across the membrane. During the translocation of Ca2+, the ATPase undergoes a complex series of reactions during which the phosphorylated intermediate EP is formed. We documented how the elementary steps of the ATPase reaction are coupled with calcium translocation, and provided evidences to indicate that two key steps of ATPase correspond to the conformational change of the enzyme, and appear to alter the affinity of the enzyme for Ca2+. A line of evidence also indicated that Ca2+-dependent ATPase of cardiac sarcoplasmic reticulum is regulated by a specific protein named phospholamban (mol.wt. 22 000), which serves as a substrate for cyclic AMP-dependent protein kinase. Cyclic AMP-dependent phosphorylation of phospholamban resulted in a marked increase in the rate of turnover of the ATPase, by enhancing the rates of the key elementary steps, i.e. the steps at which the intermediate EP is formed and decomposed. Thus phospholamban is putatively thought to serve as a modulator of Cat2+-dependent ATPase of cardiac sarcoplasmic reticulum. A working model was proposed to interpret the mechanism. Also documented is a possibility that another protein kinase activatable by Ca2+ and calmodulin is functional in regulating the phospholamban-ATPase system, thus suggesting the existence of a dual control system, in which both cyclic AMP- and calmodulin-dependent phosphorylation are in control of the Cat2+-dependent ATPase. Such a control mechanism may provide the interpretation, at the cellular level, that catecholamines exert actions on myocardial contractility. Thus, catecholamine-mediated increases in intracellular cyclic AMP could enhance calcium fluxes across the membrane of sarcoplasmic reticulum, thus resulting in the increased rates of relaxation and, at the same time, the increased rate and extent of contraction. Such a mechanism could also be operational in the tissues, other than the myocardium, in which catecholamines and other hormones serve as the ‘first messenger’, producing intracellular cyclic AMP as the ‘second messenger’.

Abstract: The effects of cannabinoids on ketogenesis in primary cultures of rat astrocytes were studied. ▵9-Tetrahydrocannabinol (THC), the major active component of marijuana, produced a malonyl-CoA-independent stimulation of carnitine palmitoyltransferase I (CPT-I) and ketogenesis from [14C]palmitate. The THC-induced stimulation of ketogenesis was mimicked by the synthetic cannabinoid HU-210 and was prevented by pertussis toxin and the CB1 cannabinoid receptor antagonist SR141716. Experiments performed with different cellular modulators indicated that the THC-induced stimulation of ketogenesis was independent of cyclic AMP, Ca2+, protein kinase C, and mitogen-activated protein kinase (MAPK). The possible involvement of ceramide in the activation of ketogenesis by cannabinoids was subsequently studied. THC produced a CB1 receptor-dependent stimulation of sphingomyelin breakdown that was concomitant to an elevation of intracellular ceramide levels. Addition of exogenous sphingomyelinase to the astrocyte culture medium led to a MAPK-independent activation of ketogenesis that was quantitatively similar and not additive to that exerted by THC. Furthermore, ceramide activated CPT-I in astrocyte mitochondria. Results thus indicate that cannabinoids stimulate ketogenesis in astrocytes by a mechanism that may rely on CB1 receptor activation, sphingomyelin hydrolysis, and ceramide-mediated activation of CPT-I.

We conducted this study to determine what receptor mediates the effect of oxytocin to increase osmotic water permeability (Pf) in the rat inner medullary collecting duct (IMCD). Reverse transcription-polymerase chain reaction (RT-PCR) experiments demonstrated that mRNA for both the oxytocin receptor and the V2 receptor is present in the rat terminal IMCD. In isolated perfused IMCD segments, we found that the V2 vasopressin receptor antagonist [d(CH2)5(1),D-Ile2,Ile4,Arg8]vasopressin, but not oxytocin receptor antagonists, blocked the hydrosmotic response to 200 pM oxytocin. The selective oxytocin receptor agonist [Thr4,Gly7]oxytocin did not increase water permeability. Oxytocin also increased urea permeability in IMCD segments. Studies in IMCD suspensions showed that oxytocin increases adenosine 3',5'-cyclic monophosphate production in a dose-dependent fashion with a half-maximal (EC50) response at 5.2 nM. The dose-response curves were virtually identical for IMCD suspension...

Glucagon-like peptide 2 (GLP-2) is an endogenous hormone with potent and specific intestinotrophic activity in vivo and in vitro. The aim of this study was to define the initial signal transduction mechanisms mediating the proliferative actions of GLP-2 on intestinal epithelial cells.The proliferative actions of GLP-2 on the human Caco-2 cell line were assessed. Specific G-protein inhibitors, pertussis and cholera toxin, were used to characterize the roles of early signal transduction mechanisms in mediating the proliferative actions of GLP-2 in these cells.GLP-2 directly stimulated proliferation in the Caco-2 cells. GLP-2 stimulated proliferation was (1) inhibited in a dose-dependent fashion by both pertussis and cholera toxin and (2) augmented by 2′,5′-dideoxyadenosine. Proliferation rates were inversely proportional to changes in intracellular cAMP concentration.Our findings suggest that a G-protein-linked signaling pathway is involved with GLP-2 bioactivity in the intestinal epithelial cell line Caco-2.

Astrocytes are involved in multiple brain functions in physiological conditions, participating in neuronal development, synaptic activity and homeostatic control of the extracellular environment. They also actively participate in the processes triggered by brain injuries, aimed at limiting and repairing brain damages. Purines may play a significant role in the pathophysiology of numerous acute and chronic disorders of the central nervous system (CNS). Astrocytes are the main source of cerebral purines. They release either adenine-based purines, e.g. adenosine and adenosine triphosphate, or guanine-based purines, e.g. guanosine and guanosine triphosphate, in physiological conditions and release even more of these purines in pathological conditions. Astrocytes express several receptor subtypes of P1 and P2 types for adenine-based purines. Receptors for guanine-based purines are being characterised. Specific ecto-enzymes such as nucleotidases, adenosine deaminase and, likely, purine nu...

The chronic stress of caregiving may lead to sympathetic nervous system activation and immune suppression. beta(2)-adrenergic receptors are expressed on all immune cells and contribute to the stress-induced loss of immune-cell function. The authors examined the effects of being a spousal caregiver of a patient with Alzheimer disease (AD) on the lymphocyte beta(2)-adrenergic receptor. One hundred and six women and men, spousal caregivers and non-caregivers, participated (mean age: 71.5 years). Caregivers were classified as either vulnerable or non-vulnerable on the basis of the amount of care required by the patient relative to the amount of respite the caregiver received during the previous 6 months. beta(2)-adrenergic receptor sensitivity (cyclic-AMP response to isoproterenol stimulation) and density (radioligand binding) were determined by use of whole lymphocytes. Vulnerable caregivers had reduced beta(2)-adrenergic receptor sensitivity and density when compared with their non-vu...