Involvement of Src tyrosine kinase and mitogen-activated protein kinase in the facilitation of calcium channels in rat nucleus of the tractus solitarius by angiotensin II

Modulation of L-type calcium channels in Alzheimer's disease: A potential therapeutic target

Calcium plays a fundamental role in various signaling pathways and cellular processes in the human organism. In the nervous system, voltage-gated calcium channels such as L-type calcium channels (LTCCs) are critical elements in mediating neurotransmitter release, synaptic integration and plasticity. Dysfunction of LTCCs has been implicated in both aging and Alzheimer's Disease (AD), constituting a key component of calcium hypothesis of AD. As such, LTCCs are a promising drug target in AD. However, due to their structural and functional complexity, the mechanisms by which LTCCs contribute to AD are still unclear. In this review, we briefly summarize the structure, function, and modulation of LTCCs that are the backbone for understanding pathological processes involving LTCCs. We suggest targeting molecular pathways up-regulating LTCCs in AD may be a more promising approach, given the diverse physiological functions of LTCCs and the ineffectiveness of LTCC blockers in clinical studies.

Angiotensin II-triggered kinase signaling cascade in the central nervous system

Recent studies have projected the renin-angiotensin system as a central component of the physiological and pathological processes of assorted neurological disorders. Its primary effector hormone, angiotensin II (Ang II), not only mediates the physiological effects of vasoconstriction and blood pressure regulation in cardiovascular disease but is also implicated in a much wider range of neuronal activities and diseases, including Alzheimer's disease, neuronal injury, and cognitive disorders. Ang II produces different actions by acting on its two subtypes of receptors (AT1 and AT2); however, the well-known physiological actions of Ang II are mainly mediated through AT1 receptors. Moreover, recent studies also suggest the important functional role of AT2 receptor in the brain. Ang II acts on AT1 receptors and conducts its functions via MAP kinases (ERK1/2, JNK, and p38MAPK), glycogen synthase kinase, Rho/ROCK kinase, receptor tyrosine kinases (PDGF and EGFR), and nonreceptor tyrosine kinases (Src, Pyk2, and JAK/STAT). AT1R-mediated NADPH oxidase activation also leads to the generation of reactive oxygen species, widely implicated in neuroinflammation. These signaling cascades lead to glutamate excitotoxicity, apoptosis, cerebral infarction, astrocyte proliferation, nociception, neuroinflammation, and progression of other neurological disorders. The present review focuses on the Ang II-triggered signal transduction pathways in central nervous system.

Src-family tyrosine kinases and the Ca2+ signal

In this review, we shall describe the rich crosstalk between non-receptor Src-family kinases (SFKs) and the Ca²⁺ transient generated in activated cells by a variety of extracellular and intracellular stimuli, resulting in diverse signaling events. The exchange of information between SFKs and Ca²⁺ is reciprocal, as it flows in both directions. These kinases are main actors in pathways leading to the generation of the Ca²⁺ signal, and reciprocally, the Ca²⁺ signal modulates SFKs activity and functions. We will cover how SFKs participate in the generation of the cytosolic Ca²⁺ rise upon activation of a series of receptors and the mechanism of clearance of this Ca²⁺ signal. The role of SFKs modulating Ca²⁺-translocating channels participating in these events will be amply discussed. Finally, the role of the Ca²⁺ sensor protein calmodulin on the activity of c-Src, and potentially on other SFKs, will be outlined as well. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Angiotensin II induces modulation of calcium channel currents in osteoblasts

Angiotensin II (Ang II) plays a major role in the maintenance of extracellular fluid volume and blood pressure. In addition to its well-established role in circulatory homeostasis, it has been implicated in the process of bone formation. Osteoblasts play a major role in bone formation, employing intracellular Ca(2+) as a second messenger to modulate hormonal responses and as a cofactor for mineralization. Voltage-dependent Ca(2+) channels (VDCCs) mediate the influx of Ca(2+) in response to membrane depolarization. The purpose of this study was to investigate the effects of Ang II on VDCC currents in osteoblasts using a patch-clamp recording method. To our knowledge, the data presented here demonstrate for the first time that Ang II facilitates VDCCs in osteoblasts.

Src kinase signaling mediates estrous behavior induced by 5β-reduced progestins, GnRH, prostaglandin E2 and vaginocervical stimulation in estrogen-primed rats

The progesterone receptor (PR) is a dual function protein that acts in the nucleus as a transcriptional factor and at the cytoplasm as a scaffold for the Src-MAPK signaling pathway. Several agents lacking affinity for the PR, such as 5β-reduced progestins, GnRH or prostaglandin E(2) (PGE(2)) facilitate estrous behavior in ovariectomized (ovx), estrogen-primed rats yet their action is blocked by the antiprogestin RU486. We hypothesize that these agents act by using the PR-Src-mitogen activated protein kinase alternative pathway. To test this hypothesis we used PP2, a specific inhibitor of the Src kinase family. Intraventricular infusion of 30 μg of PP2, 30 min before behavioral testing, significantly attenuated estrous behaviors induced in estradiol benzoate (E(2)B)-primed rats by 5β-dihydroprogesterone (5β-DHP), 5β-pregnan-3β-ol-20-one (5β,3β-Pgl), GnRH, PGE(2) and by manual flank/vaginocervical stimulation. These results suggest that the Src signaling system, by activating mitogen-activated protein kinases, participates in the facilitation of estrous behavior in E(2)B-primed rats induced by agents lacking affinity for the PR.

Calcitonin gene-related peptide- and adrenomedullin-induced facilitation of calcium current by different signal pathways in nucleus tractus solitarius

Calcitonin gene-related peptides (CGRP) and adrenomedullin (ADM) belong to the calcitonin family of peptides and are structurally related. Both peptides are found in the neurons of the CNS and play a role in many neuronal functions, including the control of blood pressure. The nucleus tractus solitarius (NTS) is known to play a major role in the regulation of cardiovascular, respiratory, gustatory, hepatic and swallowing functions. Recently, hypotension and bradycardia were observed after CGRP and ADM injection in the NTS. Voltage-dependent Ca(2+) channels (VDCCs) serve as crucial mediators of membrane excitability and Ca(2+)-dependent functions, such as neurotransmitter release, enzyme activity, and gene expression. The purpose of this study is to investigate the effects of CGRP and ADM on VDCC currents (I(Ca)) carried by Ba(2+) (I(Ba)) in the NTS, using patch-clamp recording methods. Application of CGRP and ADM caused facilitation of I(Ba) in a concentration-dependent manner. Intracellular dialysis of the anti-Galpha(s)-protein antibody attenuated CGRP-induced facilitation of I(Ba). Intracellular dialysis of the anti-Galpha(i)-protein antibody attenuated ADM-induced facilitation of I(Ba). Pretreatment with SQ22536 (an adenylate cyclase inhibitor) and intracellular dialysis of PKI(5-24) (a protein kinase A inhibitor) attenuated CGRP-induced facilitation of I(Ba). In contrast, pretreatment with PD98,059 (a mitogen-activated protein kinas inhibitor) attenuated ADM-induced facilitation of I(Ba). Mainly L-type VDCCs were facilitated by both CGRP and ADM. These results indicate that CGRP facilitates L-type VDCCs via Galpha(s)-protein involving adenylate cyclase and protein kinase A. In contrast, ADM facilitates L-type VDCCs via Galpha(i)-protein involving mitogen-activated protein kinase in the NTS.

Supramolecular assemblies and localized regulation of voltage-gated ion channels

This review addresses the localized regulation of voltage-gated ion channels by phosphorylation. Comprehensive data on channel regulation by associated protein kinases, phosphatases, and related regulatory proteins are mainly available for voltage-gated Ca2+ channels, which form the main focus of this review. Other voltage-gated ion channels and especially Kv7.1-3 (KCNQ1-3), the large- and small-conductance Ca2+-activated K+ channels BK and SK2, and the inward-rectifying K+ channels Kir3 have also been studied to quite some extent and will be included. Regulation of the L-type Ca2+ channel Cav1.2 by PKA has been studied most thoroughly as it underlies the cardiac fight-or-flight response. A prototypical Cav1.2 signaling complex containing the beta2 adrenergic receptor, the heterotrimeric G protein Gs, adenylyl cyclase, and PKA has been identified that supports highly localized via cAMP. The type 2 ryanodine receptor as well as AMPA- and NMDA-type glutamate receptors are in close proximity to Cav1.2 in cardiomyocytes and neurons, respectively, yet independently anchor PKA, CaMKII, and the serine/threonine phosphatases PP1, PP2A, and PP2B, as is discussed in detail. Descriptions of the structural and functional aspects of the interactions of PKA, PKC, CaMKII, Src, and various phosphatases with Cav1.2 will include comparisons with analogous interactions with other channels such as the ryanodine receptor or ionotropic glutamate receptors. Regulation of Na+ and K+ channel phosphorylation complexes will be discussed in separate papers. This review is thus intended for readers interested in ion channel regulation or in localization of kinases, phosphatases, and their upstream regulators.

Muscarinic M2 receptor inhibition of calcium current in rat nucleus tractus solitarius

The cholinergic system in the central nervous system plays an important role in higher brain functions, through muscarinic receptors. The nucleus tractus solitarius is known to play a major role in the regulation of cardiovascular, respiratory, gustatory, hepatic and swallowing functions. Voltage-dependent Ca2+ channels (VDCCs) serve as crucial mediators of membrane excitability and Ca2+-dependent functions such as neurotransmitter release, enzyme activity and gene expression. The purpose of this study was to investigate the effects of acetylcholine (Ach) on VDCC currents (I(Ca)) in the nucleus tractus solitarius using patch-clamp recording methods. In 68 out of 99 neurons, an application of ACh caused inhibition of N-type and P/Q-type I(Ba) in a concentration-dependent manner. Pretreatments with AF-DX116 (muscarinic M2 receptor antagonist) attenuated the ACh-induced inhibition of I(Ba). Intracellular dialysis of the Galpha(i)-protein antibody also attenuated the ACh-induced inhibition of I(Ba). These results indicate that ACh inhibits N-type and P/Q-type VDCCs via Gi-protein betagamma subunits mediated by M2 receptors in nucleus tractus solitarius.

New insights into the electrophysiology of brainstem circuits controlling blood pressure

The brainstem contains the necessary circuitry for the maintenance and regulation of arterial blood pressure. It has become increasingly clear in the past few years that the characteristics of the neurons that constitute these circuits are not static, but can be altered in the face of chronic changes in physiological state. Alterations in voltage-gated and ligand-gated ion channels have been reported in neurons located within the nucleus of the solitary tract and the nucleus ambiguus in response to hypertension and exposures to hypoxia and environmental pollutants (eg, ozone and cigarette smoke). A discussion of these neuronal adaptations, the mechanisms that might initiate and sustain the adaptations, and their potential significance is the focus of this brief review.

Dual effects of neurokinin on calcium channel currents and signal pathways in neonatal rat nucleus tractus solitarius

Neurokinins, such as substance P (SP), modulate the reflex regulation of cardiovascular and respiratory function in the CNS, particularly in the nucleus tractus solitarius (NTS). There is considerable evidence of the action of SP in the NTS, but the precise effects have not yet been determined. Voltage-dependent Ca2+ channels (VDCCs) serve as crucial mediators of membrane excitability and Ca2+ -dependent functions such as neurotransmitter release, enzyme activity and gene expression. The purpose of this study was to investigate the effects of neurokinins on VDCCs currents (ICa) in the NTS using patch-clamp recording methods. In 142 of 282 neurons, an application of [Sar(9), Met(O(2)11]-substance P (SSP, NK(1) receptor agonist) caused facilitation of L-type I(Ba). Intracellular dialysis of the Galpha(q/11)-protein antibody attenuated the SSP-induced facilitation of I(Ba). In addition, phospholipase C (PLC) inhibitor, protein kinase C (PKC) inhibitor and PKC activator attenuated the SSP-induced the facilitation of I(Ba). In contrast, in 115 of 282 neurons, an application of SSP caused inhibition of N- and P/Q-types I(Ba). Intracellular dialysis of the Gbetagamma-protein antibody attenuated the SSP-induced inhibition of I(Ba). These results indicate that NK(1) receptor facilitates L-type VDCCs via Galpha(q/11)-protein involving PKC in NTS. On the other hand, NK(1) receptor inhibits N- and P/Q-types VDCCs via Galpha(q/11)-protein betagamma subunits in NTS.

Nox2, Ca2+, and protein kinase C play a role in angiotensin II-induced free radical production in nucleus tractus solitarius

The dorsomedial portion of the nucleus tractus solitarius (dmNTS) is the site of termination of baroreceptor and cardiorespiratory vagal afferents and plays a critical role in cardiovascular regulation. Angiotensin II (Ang II) is a powerful signaling molecule in dmNTS neurons and exerts some of its biological effects by modulating Ca(2+) currents via reactive oxygen species (ROS) derived from reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase. We investigated whether a Nox2-containing NADPH oxidase is the source of the Ang II-induced ROS production and whether the signaling mechanisms of its activation require intracellular Ca(2+) or protein kinase C (PKC). Second-order dmNTS neurons were anterogradely labeled with 4-(4-[didecylamino]styryl)-N-methylpyridinium iodide transported from the vagus and isolated from the brain stem. ROS production was assessed in 4-(4-[didecylamino]styryl)-N-methylpyridinium iodide-positive dmNTS neurons using the fluorescent dye 6-carboxy-2',7'-dichlorodihydro-fluorescein di(acetoxymethyl ester). Ang II (3 to 2000 nmol/L) increased ROS production in dmNTS neurons (EC(50)=38.3 nmol/L). The effect was abolished by the ROS scavenger Mn (III) porphyrin 5,10,20-tetrakis (benzoic acid) porphyrin manganese (III), the Ang II type 1 receptor antagonist losartan, or the NADPH oxidase inhibitors apocynin or gp91ds-tat. Ang II failed to increase ROS production or to potentiate L-type Ca(2+) currents in dmNTS neurons of mice lacking Nox2. The PKC inhibitor GF109203X or depletion of intracellular Ca(2+) attenuated Ang II-elicited ROS production. We conclude that the powerful effects of Ang II on Ca(2+) currents in dmNTS neurons are mediated by PKC activation leading to ROS production via Nox2. Thus, a Nox2-containing NADPH oxidase is the critical link between Ang II and the enhancement of Ca(2+) currents that underlie the actions of Ang II on central autonomic regulation.

Pharmacological characterization of inhibitory effects of postsynaptic opioid and cannabinoid receptors on calcium currents in neonatal rat nucleus tractus solitarius

1. The profile of opioid and cannabinoid receptors in neurons of the nucleus tractus solitarius (NTS) has been studied using the whole-cell configuration of the patch clamp technique. 2. Experiments with selective agonists and antagonists of opioid, ORL and cannabinoid receptors indicated that mu-opioid, kappa-opioid, ORL-1 and CB1, but not delta-opioid, receptors inhibit VDCCs in NTS. 3. Application of [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO; mu-opioid receptor agonist), Orphanin FQ (ORL-1 receptor agonist) and WIN55,122 (CB1 receptor agonist) caused inhibition of I(Ba) in a concentration-dependent manner, with IC50's of 390 nM, 220 nM and 2.2 microM, respectively. 4. Intracellular dialysis of the G(i)-protein antibody attenuated DAMGO-, Orphanin FQ- and WIN55,122-induced inhibition of I(Ba). 5. Both pretreatment with adenylate cyclase inhibitor and intracellular dialysis of the protein kinase A (PKA) inhibitor attenuated WIN55,122-induced inhibition of I(Ba) but not DAMGO- and Orphanin FQ-induced inhibition. 6. Mainly N- and P/Q-type VDCCs were inhibited by both DAMGO and Orphanin FQ, while L-type VDCCs were inhibited by WIN55,122. 7. These results suggest that mu- and kappa-opioid receptors and ORL-1 receptor inhibit N- and P/Q-type VDCCs via G alpha(i)-protein betagamma subunits, whereas CB1 receptors inhibit L-type VDCCs via G alpha(i)-proteins involving PKA in NTS.