The continuous heart failure spectrum: moving beyond an ejection fraction classification.

Randomized clinical trials initially used heart failure (HF) patients with low left ventricular ejection fraction (LVEF) to select study populations with high risk to enhance statistical power. However, this use of LVEF in clinical trials has led to oversimplification of the scientific view of a complex syndrome. Descriptive terms such as 'HFrEF' (HF with reduced LVEF), 'HFpEF' (HF with preserved LVEF), and more recently 'HFmrEF' (HF with mid-range LVEF), assigned on arbitrary LVEF cut-off points, have gradually arisen as separate diseases, implying distinct pathophysiologies. In this article, based on pathophysiological reasoning, we challenge the paradigm of classifying HF according to LVEF. Instead, we propose that HF is a heterogeneous syndrome in which disease progression is associated with a dynamic evolution of functional and structural changes leading to unique disease trajectories creating a spectrum of phenotypes with overlapping and distinct characteristics. Moreover, we argue that by recognizing the spectral nature of the disease a novel stratification will arise from new technologies and scientific insights that will shape the design of future trials based on deeper understanding beyond the LVEF construct alone.

Angiotensin II-induced hypertension and cardiac hypertrophy are differentially mediated by TLR3- and TLR4-dependent pathways.

Toll-like receptors (TLR) are key components of the innate immune system that elicit inflammatory responses through the adaptor proteins myeloid differentiation protein 88 (MyD88) and Toll-interleukin receptor domain-containing adaptor protein-inducing interferon-ß (TRIF). Previously, we demonstrated that TRIF mediates the signaling of angiotensin II (ANG II)- induced hypertension and cardiac hypertrophy. Since TRIF is activated selectively by TLR3 and TLR4, our goals in this study were to determine the roles of TLR3 and TLR4 in mediating ANG II-induced hypertension and cardiac hypertrophy, and associated changes in proinflammatory gene expression in heart and kidney. In wild-type (WT) mice, ANG II infusion (1,000 ng·kg-1·min-1 for 3 wk) increased systolic blood pressure and caused cardiac hypertrophy. In ANG II-infused TLR4-deficient mice (Tlr4del), hypertrophy was significantly attenuated despite a preserved or enhanced hypertensive response. In contrast, in TLR3-deficient mice (Tlr3-/-), both ANG II-induced hypertension and hypertrophy were abrogated. In WT mice, ANG II increased the expression of several proinflammatory genes in hearts and kidneys that were attenuated in both TLR4- and TLR3-deficient mice compared with WT. We conclude that ANG II activates both TLR4-TRIF and TLR3-TRIF pathways in a nonredundant manner whereby hypertension is dependent on activation of the TLR3-TRIF pathway and cardiac hypertrophy is dependent on both TLR3-TRIF and TLR4-TRIF pathways. NEW & NOTEWORTHY Angiotensin II (ANG II)-induced hypertension is dependent on the endosomal Toll-like receptor 3 (TLR3)-Toll-interleukin receptor domain-containing adaptor protein-inducing interferon-ß (TRIF) pathway of the innate immune system but not on cell membrane localized TLR4. However, ANG II-induced cardiac hypertrophy is regulated by both TLR4-TRIF and TLR3-TRIF pathways. Thus, ANG II-induced rise in systolic blood pressure is independent of TLR4-TRIF effect on cardiac hypertrophy. The TLR3-TRIF pathway may be a potential target of therapeutic intervention.

Renal denervation and CD161a immune ablation prevent cholinergic hypertension and renal sodium retention.

Cholinergic receptor activation leads to premature development of hypertension and infiltration of proinflammatory CD161a+/CD68+ M1 macrophages into the renal medulla. Renal inflammation is implicated in renal sodium retention and the development of hypertension. Renal denervation is known to decrease renal inflammation. The objective of this study was to determine the role of CD161a+/CD68+ macrophages and renal sympathetic nerves in cholinergic-hypertension and renal sodium retention. Bilateral renal nerve denervation (RND) and immune ablation of CD161a+ immune cells were performed in young prehypertensive spontaneously hypertensive rat (SHR) followed by infusion of either saline or nicotine (15 mg·kg-1·day-1) for 2 wk. Immune ablation was conducted by injection of unconjugated azide-free antibody targeting rat CD161a+. Blood pressure was monitored by tail cuff plethysmography. Tissues were harvested at the end of infusion. Nicotine induced premature hypertension, renal expression of the sodium-potassium chloride cotransporter (NKCC2), increases in renal sodium retention, and infiltration of CD161a+/CD68+ macrophages into the renal medulla. All of these effects were abrogated by RND and ablation of CD161a+ immune cells. Cholinergic activation of CD161a+ immune cells with nicotine leads to the premature development of hypertension in SHR. The effects of renal sympathetic nerves on chemotaxis of CD161a+ macrophages to the renal medulla, increased renal expression of NKCC2, and renal sodium retention contribute to cholinergic hypertension. The CD161a+ immune cells are necessary and essential for this prohypertensive nicotine-mediated inflammatory response.NEW & NOTEWORTHY This is the first study that describes a novel integrative physiological interaction between the adrenergic, cholinergic, and renal systems in the development of hypertension, describing data for the role of each in a genetic model of essential hypertension. Noteworthy findings include the prevention of nicotine-mediated hypertension following successful immune ablation of CD161a+ immune cells and the necessary role these cells play in the overexpression of the sodium-potassium-chloride cotransporter (NKCC2) in the renal medulla and renal sodium retention. Renal infiltration of these cells is demonstrated to be dependent on the presence of renal adrenergic innervation. These data offer a fertile ground of therapeutic potential for the treatment of hypertension as well as open the door for further investigation into the mechanism involved in inflammation-mediated renal sodium transporter expression. Taken together, these findings suggest immune therapy, renal denervation, and, possibly, other new molecular targets as having a potential role in the development and maintenance of essential hypertension.

Relative burst amplitude of muscle sympathetic nerve activity is an indicator of altered sympathetic outflow in chronic anxiety.

Relative burst amplitude of muscle sympathetic nerve activity (MSNA) is an indicator of augmented sympathetic outflow and contributes to greater vasoconstrictor responses. Evidence suggests anxiety-induced augmentation of relative MSNA burst amplitude in patients with panic disorder; thus we hypothesized that acute stress would result in augmented relative MSNA burst amplitude and vasoconstriction in individuals with chronic anxiety. Eighteen participants with chronic anxiety (ANX; 8 men, 10 women, 32 ± 2 yr) and 18 healthy control subjects with low or no anxiety (CON; 8 men, 10 women, 39 ± 3 yr) were studied. Baseline MSNA and 24-h blood pressure were similar between ANX and CON ( P > 0.05); however, nocturnal systolic blood pressure % dipping was blunted among ANX ( P = 0.02). Relative MSNA burst amplitude was significantly greater among ANX compared with CON immediately preceding (anticipation) and during physiological stress [2-min cold pressor test; ANX: 73 ± 5 vs. CON: 59 ± 3% arbitrary units (AU), P = 0.03] and mental stress (4-min mental arithmetic; ANX: 65 ± 3 vs. CON: 54 ± 3% AU, P = 0.02). Increases in MSNA burst frequency, incidence, and total activity in response to stress were not augmented among ANX compared with CON ( P > 0.05), and reduction in brachial artery conductance during cold stress was similar between ANX and CON ( P = 0.92). Relative MSNA burst amplitude during mental stress was strongly correlated with state ( P < 0.01) and trait ( P = 0.01) anxiety (State-Trait Anxiety Inventory), independent of age, sex, and body mass index. Thus in response to acute stress, both mental and physiological, individuals with chronic anxiety demonstrate selective augmentation in relative MSNA burst amplitude, indicating enhanced sympathetic drive in a population with higher risk for cardiovascular disease. NEW & NOTEWORTHY Relative burst amplitude of muscle sympathetic nerve activity in response to acute mental and physiological stress is selectively augmented in individuals with chronic anxiety, which is a prevalent condition that is associated with the development of cardiovascular disease. Augmented sympathetic burst amplitude occurs with chronic anxiety in the absence of common comorbidities. These findings provide important insight into the relation between anxiety, acute stress and sympathetic activation.

Nicotine Mediates CD161a+ Renal Macrophage Infiltration and Premature Hypertension in the Spontaneously Hypertensive Rat.

RATIONALE: Renal inflammation contributes to the pathophysiology of hypertension. CD161a+ immune cells are dominant in the (SHR) spontaneously hypertensive rat and expand in response to nicotinic cholinergic activation. OBJECTIVE: We aimed to phenotype CD161a+ immune cells in prehypertensive SHR after cholinergic activation with nicotine and determine if these cells are involved in renal inflammation and the development of hypertension. METHODS AND RESULTS: Studies used young SHR and WKY (Wistar-Kyoto) rats. Splenocytes and bone marrow cells were exposed to nicotine ex vivo, and nicotine was infused in vivo. Blood pressures, kidney, serum, and urine were obtained. Flow cytometry, Luminex/ELISA, immunohistochemistry, confocal microscopy, and Western blot were used. Nicotinic cholinergic activation induced proliferation of CD161a+/CD68+ macrophages in SHR-derived splenocytes, their renal infiltration, and premature hypertension in SHR. These changes were associated with increased renal expression of MCP-1 (monocyte chemoattractant protein-1) and VLA-4 (very-late antigen-4). LLT1 (lectin-like transcript 1), the ligand for CD161a, was overexpressed in SHR kidney, whereas vascular cellular and intracellular adhesion molecules were similar to those in WKY. Inflammatory cytokines were elevated in SHR kidney and urine after nicotine infusion. Nicotine-mediated renal macrophage infiltration/inflammation was enhanced in denervated kidneys, not explained by angiotensin II levels or expression of angiotensin type-1/2 receptors. Moreover, expression of the anti-inflammatory α7-nAChR (α7-nicotinic acetylcholine receptor) was similar in young SHR and WKY rats. CONCLUSIONS: A novel, inherited nicotinic cholinergic inflammatory effect exists in young SHR, measured by expansion of CD161a+/CD68+ macrophages. This leads to renal inflammation and premature hypertension, which may be partially explained by increased renal expression of LLT-1, MCP-1, and VLA-4.

Abnormal CD161+ immune cells and retinoic acid receptor-related orphan receptor γt-mediate enhanced IL-17F expression in the setting of genetic hypertension.

BACKGROUND: Hypertension is considered an immunologic disorder. However, the role of the IL-17 family in genetic hypertension in the spontaneously hypertensive rat (SHR) has not been investigated. OBJECTIVE: We tested the hypothesis that enhanced TH17 programming and IL-17 expression in abundant CD161+ immune cells in SHRs represent an abnormal proinflammatory adaptive immune response. Furthermore, we propose that this response is driven by the master regulator retinoic acid receptor-related orphan receptor γt (RORγt) and a nicotinic proinflammatory innate immune response. METHODS: We measured expression of the CD161 surface marker on splenocytes in SHRs and normotensive control Wistar-Kyoto (WKY) rats from birth to adulthood. We compared expression of IL-17A and IL-17F in splenic cells under different conditions. We then determined the functional effect of these cytokines on vascular reactivity. Finally, we tested whether pharmacologic inhibition of RORγt can attenuate hypertension in SHRs. RESULTS: SHRs exhibited an abnormally large population of CD161+ cells at birth that increased with age, reaching more than 30% of the splenocyte population at 38 weeks. The SHR splenocytes constitutively expressed more RORγt than those of WKY rats and produced more IL-17F on induction. Exposure of WKY rat aortas to IL-17F impaired endothelium-dependent vascular relaxation, whereas IL-17A did not. Moreover, in vivo inhibition of RORγt by digoxin decreased systolic blood pressure in SHRs. CONCLUSIONS: SHRs have a markedly enhanced potential for RORγt-driven expression of proinflammatory and prohypertensive IL-17F in response to innate immune activation. Increased RORγt and IL-17F levels contribute to SHR hypertension and might be therapeutic targets.

Autonomic regulation of the immune system in cardiovascular diseases.

The autonomic nervous system is a powerful regulator of circulatory adjustments to acute hemodynamic stresses. Here we focus on new concepts that emphasize the chronic influence of the sympathetic and parasympathetic systems on cardiovascular pathology. The autonomic neurohumoral system can dramatically influence morbidity and mortality from cardiovascular disease through newly discovered influences on the innate and adaptive immune systems. Specifically, the end-organ damage in heart failure or hypertension may be worsened or alleviated by pro- or anti-inflammatory pathways of the immune system, respectively, that are activated through neurohumoral transmitters. These concepts provide a major new perspective on potentially life-saving therapeutic interventions in the deadliest of diseases.

Toll-like receptors and hypertension.

Hypertension and associated inflammatory processes that accelerate cardiovascular damage are regulated by the innate immune system. Toll-like receptors (TLR) are major components of the innate immune system that recognize endogenous damage-associated molecular patterns to activate prominent inflammatory signaling including activation of nuclear factor-κB (NF-κB). However, the role of TLR in the etiology of hypertension is not well understood. TLR signaling is dependent on adaptor proteins that, along with the TLR expression patterns, confer specificity of the inflammatory response and its pathological targets. Here we review the conceptual framework of how TLR and their adaptor proteins may differentially affect hypertension and cardiac hypertrophy by different stimuli.

Neurohormonal modulation of the innate immune system is proinflammatory in the prehypertensive spontaneously hypertensive rat, a genetic model of essential hypertension.

RATIONALE: Inflammation and autonomic dysfunction contribute to the pathophysiology of hypertension. Cholinergic stimulation suppresses innate immune responses. Angiotensin II (Ang II) induces hypertension and is associated with proinflammatory immune responses. OBJECTIVE: Our goal was to define the innate immune response in a model of genetic hypertension and the influences of cholinergic stimulation and Ang II. METHODS AND RESULTS: Studies were conducted on 4- to 5-week-old prehypertensive spontaneously hypertensive rats (SHRs) and age-matched normotensive control, Wistar Kyoto (WKY) rats. Isolated splenocytes were preexposed to nicotine or Ang II before Toll-like receptor (TLR) activation. Culture supernatants were tested for cytokines (tumor necrosis factor-α, interleukin [IL]-10, and IL-6). TLR-mediated cytokine responses were most pronounced with TLR7/8 and TLR9 activation and similar between WKY rats and SHRs. Nicotine and Ang II enhanced this TLR-mediated IL-6 response in prehypertensive SHR splenocytes. In contrast, nicotine suppressed the TLR-mediated IL-6 response in WKY rats, whereas Ang II had no effect. In vivo, nicotine enhanced plasma levels of TLR7/8-mediated IL-6 and IL-1ß responses in prehypertensive SHRs but suppressed these responses in WKY rats. Flow cytometry revealed an increase in a CD161+ innate immune cell population, which was enhanced by nicotine in the prehypertensive SHR spleen but not in WKY. CONCLUSIONS: There is a pronounced anti-inflammatory nicotinic/cholinergic modulation of the innate immune system in WKY rats, which is reversed in prehypertensive SHRs. The results support the novel concept that neurohormonal regulation of the innate immune system plays a role in the pathogenesis of genetic hypertension and provide putative molecular targets for treatment of hypertension.

Responses of glomus cells to hypoxia and acidosis are uncoupled, reciprocal and linked to ASIC3 expression: selectivity of chemosensory transduction.

Carotid body glomus cells are the primary sites of chemotransduction of hypoxaemia and acidosis in peripheral arterial chemoreceptors. They exhibit pronounced morphological heterogeneity. A quantitative assessment of their functional capacity to differentiate between these two major chemical signals has remained undefined. We tested the hypothesis that there is a differential sensory transduction of hypoxia and acidosis at the level of glomus cells. We measured cytoplasmic Ca(2+) concentration in individual glomus cells, isolated in clusters from rat carotid bodies, in response to hypoxia ( mmHg) and to acidosis at pH 6.8. More than two-thirds (68%) were sensitive to both hypoxia and acidosis, 19% were exclusively sensitive to hypoxia and 13% exclusively sensitive to acidosis. Those sensitive to both revealed significant preferential sensitivity to either hypoxia or to acidosis. This uncoupling and reciprocity was recapitulated in a mouse model by altering the expression of the acid-sensing ion channel 3 (ASIC3) which we had identified earlier in glomus cells. Increased expression of ASIC3 in transgenic mice increased pH sensitivity while reducing cyanide sensitivity. Conversely, deletion of ASIC3 in the knockout mouse reduced pH sensitivity while the relative sensitivity to cyanide or to hypoxia was increased. In this work, we quantify functional differences among glomus cells and show reciprocal sensitivity to acidosis and hypoxia in most glomus cells. We speculate that this selective chemotransduction of glomus cells by either stimulus may result in the activation of different afferents that are preferentially more sensitive to either hypoxia or acidosis, and thus may evoke different and more specific autonomic adjustments to either stimulus.

Acid sensing ion channels regulate neuronal excitability by inhibiting BK potassium channels.

Acid sensing ion channels (ASICs), Ca(2+) and voltage-activated potassium channels (BK) are widely present throughout the central nervous system. Previous studies have shown that when expressed together in heterologous cells, ASICs inhibit BK channels, and this inhibition is relieved by acidic extracellular pH. We hypothesized that ASIC and BK channels might interact in neurons, and that ASICs may regulate BK channel activity. We found that ASICs inhibited BK currents in cultured wild-type cortical neurons, but not in ASIC1a/2/3 triple knockout neurons. The inhibition in the wild-type was partially relieved by a drop in extracellular pH to 6. To test the consequences of ASIC-BK interaction for neuronal excitability, we compared action potential firing in cultured cortical neurons from wild-type and ASIC1a/2/3 null mice. We found that in the knockout, action potentials were narrow and exhibited increased after-hyperpolarization. Moreover, the excitability of these neurons was significantly increased. These findings are consistent with increased BK channel activity in the neurons from ASIC1a/2/3 null mice. Our data suggest that ASICs can act as endogenous pH-dependent inhibitors of BK channels, and thereby can reduce neuronal excitability.

Chemoreceptor hypersensitivity, sympathetic excitation, and overexpression of ASIC and TASK channels before the onset of hypertension in SHR.

RATIONALE: Increased sympathetic nerve activity has been linked to the pathogenesis of hypertension in humans and animal models. Enhanced peripheral chemoreceptor sensitivity which increases sympathetic nerve activity has been observed in established hypertension but has not been identified as a possible mechanism for initiating an increase in sympathetic nerve activity before the onset of hypertension. OBJECTIVE: We tested this hypothesis by measuring the pH sensitivity of isolated carotid body glomus cells from young spontaneously hypertensive rats (SHR) before the onset of hypertension and their control normotensive Wistar-Kyoto (WKY) rats. METHODS AND RESULTS: We found a significant increase in the depolarizing effect of low pH in SHR versus WKY glomus cells which was caused by overexpression of 2 acid-sensing non-voltage-gated channels. One is the amiloride-sensitive acid-sensing sodium channel (ASIC3), which is activated by low pH and the other is the 2-pore domain acid-sensing K(+) channel (TASK1), which is inhibited by low pH and blocked by quinidine. Moreover, we found that the increase in sympathetic nerve activity in response to stimulation of chemoreceptors with sodium cyanide was markedly enhanced in the still normotensive young SHR compared to control WKY rats. CONCLUSIONS: Our results establish a novel molecular basis for increased chemotransduction that contributes to excessive sympathetic activity before the onset of hypertension.

ASIC2a and ASIC3 heteromultimerize to form pH-sensitive channels in mouse cardiac dorsal root ganglia neurons.

RATIONALE: Acid-sensing ion channels (ASICs) are Na+ channels that are activated by acidic pH. Their expression in cardiac afferents and remarkable sensitivity to small pH changes has made them leading candidates to sense cardiac ischemia. OBJECTIVE: Four genes encode six different ASIC subunits, however it is not yet clear which of the ASIC subunits contribute to the composition of ASICs in cardiac afferents. METHODS AND RESULTS: Here, we labeled cardiac afferents using a retrograde tracer dye in mice, which allowed for patch-clamp studies of murine cardiac afferents. We found that a higher percentage of cardiac sensory neurons from the dorsal root ganglia respond to acidic pH and generated larger currents compared to those from the nodose ganglia. The ASIC-like current properties of the cardiac dorsal root ganglia neurons from wild-type mice most closely matched the properties of ASIC2a/3 heteromeric channels. This was supported by studies in ASIC-null mice: acid-evoked currents from ASIC3(-/-) cardiac afferents matched the properties of ASIC2a channels, and currents from ASIC2(-/-) cardiac afferents matched the properties of ASIC3 channels. CONCLUSIONS: We conclude that ASIC2a and -3 are the major ASIC subunits in cardiac dorsal root ganglia neurons and provide potential molecular targets to attenuate chest pain and deleterious reflexes associated with cardiac disease.

Acid-sensing ion channels interact with and inhibit BK K+ channels.

Acid-sensing ion channels (ASICs) are neuronal non-voltage-gated cation channels that are activated when extracellular pH falls. They contribute to sensory function and nociception in the peripheral nervous system, and in the brain they contribute to synaptic plasticity and fear responses. Some of the physiologic consequences of disrupting ASIC genes in mice suggested that ASIC channels might modulate neuronal function by mechanisms in addition to their H(+)-evoked opening. Within ASIC channel's large extracellular domain, we identified sequence resembling that in scorpion toxins that inhibit K(+) channels. Therefore, we tested the hypothesis that ASIC channels might inhibit K(+) channel function by coexpressing ASIC1a and the high-conductance Ca(2+)- and voltage-activated K(+) (BK) channel. We found that ASIC1a associated with BK channels and inhibited their current. Reducing extracellular pH disrupted the association and relieved the inhibition. BK channels, in turn, altered the kinetics of ASIC1a current. In addition to BK, ASIC1a inhibited voltage-gated Kv1.3 channels. Other ASIC channels also inhibited BK, although acidosis-dependent relief of inhibition varied. These results reveal a mechanism of ion channel interaction and reciprocal regulation. Finding that a reduced pH activated ASIC1a and relieved BK inhibition suggests that extracellular protons may enhance the activity of channels with opposing effects on membrane voltage. The wide and varied expression patterns of ASICs, BK, and related K(+) channels suggest broad opportunities for this signaling system to alter neuronal function.

Altering Early Life Gut Microbiota Has Long-Term Effect on Immune System and Hypertension in Spontaneously Hypertensive Rats.

Hypertension is regulated by immunological components. Spontaneously hypertensive rats (SHR) display a large population of proinflammatory CD161 + immune cells. We investigated the effect of early post-natal gut microbiota on the development of the immune system and resulting hypertension in the SHR. We first examined the microbial populations in the fecal samples of SHR and normotensive control WKY using 16S rDNA sequencing. We found that in the newborn SHR (1-week old) the gut microbiota was qualitatively and quantitatively different from the newborns of normotensive WKY. The representation of the predominant bacterial phylum Proteobacteria was significantly less in 1-week old SHR pups than in WKY (94.5% Proteobacteria in WKY vs. 65.2% in SHR neonates). Even within the phylum Proteobacteria, the colonizing genera in WKY and SHR differed dramatically. Whereas WKY microbiota was predominantly comprised of Escherichia-Shigella, SHR microbiota was represented by other taxa of Enterobacteriaceae and Pasteurellaceae. In contrast, the representation of phylum Firmicutes in the neonatal SHR gut was greater than WKY. Cross-fostering newborn SHR pups by lactating WKY dams caused a dramatic shift in 1-week old cross-fostered SHR gut microbiota. The two major bacterial taxa of phylum Proteobacteria, Enterobacteriaceae and Pasteurellaceae as well as Lactobacillus intestinalis, Proteus, Romboustia and Rothia were depleted after cross-fostering and were replaced by the predominant genera of WKY (Escherichia-Shigella). A proinflammatory IL-17F producing CD161 + immune cell population in the spleen and aorta of cross-fostered SHR was also reduced (30.7% in self-fostered SHR vs. 12.6% in cross-fostered SHR at 30 weeks of age) as was the systolic blood pressure in adult cross-fostered SHR at 10 weeks of age. Thus, altered composition of gut microbiota of SHR toward WKY at early neonatal age had a long-lasting effect on immune system by reducing proinflammatory immune cells and lowering systolic blood pressure.

The Walter B. Cannon Memorial Award Lecture, 2009. Physiology in perspective: The wisdom of the body. In search of autonomic balance: the good, the bad, and the ugly.

Walter B. Cannon's research on the sympathetic nervous system and neurochemical transmission was pioneering. Wisdom has endowed our body with a powerful autonomic neural regulation of the circulation that provides optimal perfusion of every organ in accordance to its metabolic needs. Exquisite sensors tuned to an optimal internal environment trigger central and peripheral sympathetic and parasympathetic motor neurons and allow desirable and beneficial adjustments to physiologic needs as well as to acute cardiovascular stresses. This short review, presented as The Walter B. Cannon Memorial Award Lecture for 2009, addresses the mechanisms that disrupt sensory signaling and result in a chronic maladjustment of the autonomic neural output that in many cardiovascular diseases results in excessive increases in the risks of dying. The hopes for any reduction of those risks resides in an understanding of the molecular determinants of neuronal signaling.

Acid-sensing ion channels contribute to transduction of extracellular acidosis in rat carotid body glomus cells.

Carotid body chemoreceptors sense hypoxemia, hypercapnia, and acidosis and play an important role in cardiorespiratory regulation. The molecular mechanism of pH sensing by chemoreceptors is not clear, although it has been proposed to be mediated by a drop in intracellular pH of carotid body glomus cells, which inhibits a K+ current. Recently, pH-sensitive ion channels have been described in glomus cells that respond directly to extracellular acidosis. In this study, we investigated the possible molecular mechanisms of carotid body pH sensing by recording the responses of glomus cells isolated from rat carotid body to rapid changes in extracellular pH using the whole-cell patch-clamping technique. Extracellular acidosis evoked transient inward current in glomus cells that was inhibited by the acid-sensing ion channel (ASIC) blocker amiloride, absent in Na+-free bathing solution, and enhanced by either Ca2+-free buffer or addition of lactate. In addition, ASIC1 and ASIC3 were shown to be expressed in rat carotid body by quantitative PCR and immunohistochemistry. In the current-clamp mode, extracellular acidosis evoked both a transient and sustained depolarizations. The initial transient component of depolarization was blocked by amiloride, whereas the sustained component was eliminated by removal of K+ from the pipette solution and partially blocked by the TASK (tandem-p-domain, acid-sensitive K+ channel) blockers anandamide and quinidine. The results provide the first evidence that ASICs may contribute to chemotransduction of low pH by carotid body chemoreceptors and that extracellular acidosis directly activates carotid body chemoreceptors through both ASIC and TASK channels.

Increased receptor activity-modifying protein 1 in the nervous system is sufficient to protect against autonomic dysregulation and hypertension.

Calcitonin gene-related peptide (CGRP) can cause migraines, yet it is also a potent vasodilator that protects against hypertension. Given the emerging role of CGRP-targeted antibodies for migraine prevention, an important question is whether the protective actions of CGRP are mediated by vascular or neural CGRP receptors. To address this, we have characterized the cardiovascular phenotype of transgenic nestin/hRAMP1 mice that have selective elevation of a CGRP receptor subunit in the nervous system, human receptor activity-modifying protein 1 (hRAMP1). Nestin/hRAMP1 mice had relatively little hRAMP1 RNA in blood vessels and intravenous injection of CGRP caused a similar blood pressure decrease in transgenic and control mice. At baseline, nestin/hRAMP1 mice exhibited similar mean arterial pressure, heart rate, baroreflex sensitivity, and sympathetic vasomotor tone as control mice. We previously reported that expression of hRAMP1 in all tissues favorably improved autonomic regulation and attenuated hypertension induced by angiotensin II (Ang II). Similarly, in nestin/hRAMP1 mice, hypertension caused by Ang II or phenylephrine was greatly attenuated, and associated autonomic dysregulation and increased sympathetic vasomotor tone were diminished or abolished. We conclude that increased expression of neuronal CGRP receptors is sufficient to induce a protective change in cardiovascular autonomic regulation with implications for migraine therapy.