Electrocalcium coupling in brain capillaries: Rapidly traveling electrical signals ignite local calcium signals.

The routing of blood flow throughout the brain vasculature is precisely controlled by mechanisms that serve to maintain a fine balance between local neuronal demands and vascular supply of nutrients. We recently identified two capillary endothelial cell (cEC)-based mechanisms that control cerebral blood flow in vivo: 1) electrical signaling, mediated by extracellular K-dependent activation of strong inward rectifying K (Kir2.1) channels, which are steeply activated by hyperpolarization and thus are capable of cell-to-cell propagation, and 2) calcium (Ca) signaling, which reflects release of Ca via the inositol 1,4,5-trisphosphate receptor (IPR)-a target of G-protein-coupled receptor signaling.

Urothelium-derived prostanoids enhance contractility of urinary bladder smooth muscle and stimulate bladder afferent nerve activity in the mouse.

The transitional epithelial cells (urothelium) that line the lumen of the urinary bladder form a barrier between potentially harmful pathogens, toxins, and other bladder contents and the inner layers of the bladder wall. The urothelium, however, is not simply a passive barrier, as it can produce signaling factors, such as ATP, nitric oxide, prostaglandins, and other prostanoids, that can modulate bladder function. We investigated whether substances produced by the urothelium could directly modulate the contractility of the underlying urinary bladder smooth muscle.

Intraluminal pressure elevates intracellular calcium and contracts CNS pericytes: Role of voltage-dependent calcium channels.

Arteriolar smooth muscle cells (SMCs) and capillary pericytes dynamically regulate blood flow in the central nervous system in the face of fluctuating perfusion pressures. Pressure-induced depolarization and Ca elevation provide a mechanism for regulation of SMC contraction, but whether pericytes participate in pressure-induced changes in blood flow remains unknown. Here, utilizing a pressurized whole-retina preparation, we found that increases in intraluminal pressure in the physiological range induce contraction of both dynamically contractile pericytes in the arteriole-proximate transition zone and distal pericytes of the capillary bed.

Afferent nerve activity in a mouse model increases with faster bladder filling rates in vitro, but voiding behavior remains unaltered in vivo.

Storage and voiding functions in urinary bladder are well-known, yet fundamental physiological events coordinating these behaviors remain elusive. We sought to understand how voiding function is influenced by the rate at which the bladder fills. We hypothesized that faster filling rates would increase afferent sensory activity and increase micturition rate.

Adenosine signaling activates ATP-sensitive K channels in endothelial cells and pericytes in CNS capillaries.

The dense network of capillaries composed of capillary endothelial cells (cECs) and pericytes lies in close proximity to all neurons, ideally positioning it to sense neuron- and glial-derived compounds that enhance regional and global cerebral perfusion. The membrane potential () of vascular cells serves as the physiological bridge that translates brain activity into vascular function. In other beds, the ATP-sensitive K (K) channel regulates in vascular smooth muscle, which is absent in the capillary network.

The Role of PIEZO1 in Urinary Bladder Function and Dysfunction in a Rodent Model of Cyclophosphamide-Induced Cystitis.

In the urinary bladder, mechanosensitive ion channels (MSCs) underlie the transduction of bladder stretch into sensory signals that are relayed to the PNS and CNS. PIEZO1 is a recently identified MSC that is Ca permeable and is widely expressed throughout the lower urinary tract. Recent research indicates that PIEZO1 is activated by mechanical stretch or by pharmacological agonism via Yoda1.

TRPV4 blockade reduces voiding frequency, ATP release, and pelvic sensitivity in mice with chronic urothelial overexpression of NGF.

Transient receptor potential vanilloid family member 4 (TRPV4) transcript and protein expression increased in the urinary bladder and lumbosacral dorsal root ganglia of transgenic mice with chronic urothelial overexpression of nerve growth factor (NGF-OE). We evaluated the functional role of TRPV4 in bladder function with open-outlet cystometry, void spot assays, and natural voiding (Urovoid) assays with the TRPV4 antagonist HC-067047 (1 μM) or vehicle in NGF-OE and littermate wild-type (WT) mice. Blockade of TRPV4 at the level of the urinary bladder significantly ( ≤ 0.

The K 7 channel activator retigabine suppresses mouse urinary bladder afferent nerve activity without affecting detrusor smooth muscle K channel currents.

Key Points: K 7 channels are a family of voltage-dependent K channels expressed in many cell types, which open in response to membrane depolarization to regulate cell excitability. Drugs that target K 7 channels are used clinically to treat epilepsy. Interestingly, these drugs also cause urinary retention, but it was unclear how.

Development of stress-induced bladder insufficiency requires functional TRPV1 channels.

Social stress causes profound urinary bladder dysfunction in children that often continues into adulthood. We previously discovered that the intensity and duration of social stress influences whether bladder dysfunction presents as overactivity or underactivity. The transient receptor potential vanilloid type 1 (TRPV1) channel is integral in causing stress-induced bladder overactivity by increasing bladder sensory outflow, but little is known about the development of stress-induced bladder underactivity.

PACAP38-Mediated Bladder Afferent Nerve Activity Hyperexcitability and Ca Activity in Urothelial Cells from Mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1) and its cognate PAC1 receptor (Adcyap1r1) have tissue-specific distributions in the lower urinary tract (LUT). The afferent limb of the micturition reflex is often compromised following bladder injury, disease, and inflammatory conditions. We have previously demonstrated that PACAP signaling contributes to increased voiding frequency and decreased bladder capacity with cystitis.

Rhythmic Calcium Events in the Lamina Propria Network of the Urinary Bladder of Rat Pups.

The lamina propria contains a dense network of cells, including interstitial cells (ICs), that may play a role in bladder function by modulating communication between urothelium, nerve fibers and smooth muscle or acting as pacemakers. Transient receptor potential vanilloid 4 (TRPV4) channels allow cation influx and may be involved in sensing stretch or chemical irritation in urinary bladder. Urothelium was removed from rats (P0-Adult), cut into strips, and loaded with a Ca fluorescent dye (Fluo-2 AM leak resistant or Cal 520) for 90 min (35-37°C) to measure Ca events.

Lack of direct effect of adiponectin on vascular smooth muscle cell BK channels or Ca signaling in the regulation of small artery pressure-induced constriction.

The aim of this study was to investigate mechanisms by which adiponectin influences vascular Ca signaling, K channel activity and thus contractile tone of small arteries. Vasodilation to adiponectin was studied in mesenteric resistance arteries constricted with intraluminal pressure. Ca signals were characterized using high speed confocal microscopy of intact arteries.

Inhibition of vascular smooth muscle inward-rectifier K channels restores myogenic tone in mouse urinary bladder arterioles.

Prolonged decreases in urinary bladder blood flow are linked to overactive and underactive bladder pathologies. However, the mechanisms regulating bladder vascular reactivity are largely unknown. To investigate these mechanisms, we examined myogenic and vasoactive properties of mouse bladder feed arterioles (BFAs).

Purinergic signalling underlies transforming growth factor-β-mediated bladder afferent nerve hyperexcitability.

Key Points: The sensory components of the urinary bladder are responsible for the transduction of bladder filling and are often impaired with neurological injury or disease. Elevated extracellular ATP contributes, in part, to bladder afferent nerve hyperexcitability during urinary bladder inflammation or irritation. Transforming growth factor-β1 (TGF-β1) may stimulate ATP release from the urothelium through vesicular exocytosis mechanisms with minimal contribution from pannexin-1 channels to increase bladder afferent nerve discharge.

Transient contractions of urinary bladder smooth muscle are drivers of afferent nerve activity during filling.

Activation of afferent nerves during urinary bladder (UB) filling conveys the sensation of UB fullness to the central nervous system (CNS). Although this sensory outflow is presumed to reflect graded increases in pressure associated with filling, UBs also exhibit nonvoiding, transient contractions (TCs) that cause small, rapid increases in intravesical pressure. Here, using an ex vivo mouse bladder preparation, we explored the relative contributions of filling pressure and TC-induced pressure transients to sensory nerve stimulation.

Social stress in mice induces urinary bladder overactivity and increases TRPV1 channel-dependent afferent nerve activity.

Social stress has been implicated as a cause of urinary bladder hypertrophy and dysfunction in humans. Using a murine model of social stress, we and others have shown that social stress leads to bladder overactivity. Here, we show that social stress leads to bladder overactivity, increased bladder compliance, and increased afferent nerve activity.

Opposing roles of smooth muscle BK channels and ryanodine receptors in the regulation of nerve-evoked constriction of mesenteric resistance arteries.

In depolarized smooth muscle cells of pressurized cerebral arteries, ryanodine receptors (RyRs) generate "Ca2+ sparks" that activate large-conductance, Ca2+ -, and voltage-sensitive potassium (BK) channels to oppose pressure-induced (myogenic) constriction. Here, we show that BK channels and RyRs have opposing roles in the regulation of arterial tone in response to sympathetic nerve activation by electrical field stimulation. Inhibition of BK channels with paxilline increased both myogenic and nerve-induced constrictions of pressurized, resistance-sized mesenteric arteries from mice.

Elementary Ca2+ signals through endothelial TRPV4 channels regulate vascular function.

Major features of the transcellular signaling mechanism responsible for endothelium-dependent regulation of vascular smooth muscle tone are unresolved. We identified local calcium (Ca(2+)) signals ("sparklets") in the vascular endothelium of resistance arteries that represent Ca(2+) influx through single TRPV4 cation channels. Gating of individual TRPV4 channels within a four-channel cluster was cooperative, with activation of as few as three channels per cell causing maximal dilation through activation of endothelial cell intermediate (IK)- and small (SK)-conductance, Ca(2+)-sensitive potassium (K(+)) channels.

Sympathetic nerve stimulation induces local endothelial Ca2+ signals to oppose vasoconstriction of mouse mesenteric arteries.

It is generally accepted that the endothelium regulates vascular tone independent of the activity of the sympathetic nervous system. Here, we tested the hypothesis that the activation of sympathetic nerves engages the endothelium to oppose vasoconstriction. Local inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) signals ("pulsars") in or near endothelial projections to vascular smooth muscle (VSM) were measured in an en face mouse mesenteric artery preparation.

Calcium signaling in smooth muscle.

Changes in intracellular Ca(2+) are central to the function of smooth muscle, which lines the walls of all hollow organs. These changes take a variety of forms, from sustained, cell-wide increases to temporally varying, localized changes. The nature of the Ca(2+) signal is a reflection of the source of Ca(2+) (extracellular or intracellular) and the molecular entity responsible for generating it.

Unique properties of muscularis mucosae smooth muscle in guinea pig urinary bladder.

The muscularis mucosae, a type of smooth muscle located between the urothelium and the urinary bladder detrusor, has been described, although its properties and role in bladder function have not been characterized. Here, using mucosal tissue strips isolated from guinea pig urinary bladders, we identified spontaneous phasic contractions (SPCs) that appear to originate in the muscularis mucosae. This smooth muscle layer exhibited Ca(2+) waves and flashes, but localized Ca(2+) events (Ca(2+) sparks, purinergic receptor-mediated transients) were not detected.

A non-anesthetized mouse model for recording sensory urinary bladder activity.

The goal of this study was to develop an in vivo awake mouse model for extracellular bladder sensory nerve recording. A bipolar 125-μm silver electrode was positioned under a single postganglionic bladder nerve. Efferent nerve signals were eliminated by tying off the postganglionic bladder nerve between the major pelvic ganglion and the recording electrode.

Nerve-released acetylcholine contracts urinary bladder smooth muscle by inducing action potentials independently of IP3-mediated calcium release.

Nerve-released ACh is the main stimulus for contraction of urinary bladder smooth muscle (UBSM). Here, the mechanisms by which ACh contracts UBSM are explored by determining Ca(2+) and electrical signals induced by nerve-released ACh. Photolysis of caged inositol 1,4,5-trisphosphate (IP(3)) evoked Ca(2+) release from the sarcoplasmic reticulum.

Effect of endogenous and exogenous nitric oxide on calcium sparks as targets for vasodilation in rat cerebral artery.

The potent vasodilator nitric oxide (NO), produced mainly by the endothelium, acts through a BK(Ca)-dependent mechanism to increase the frequency of calcium sparks (Ca(2+) sparks) in myocyte isolated from rat cerebral arteries. Our present aim has been to assess the role of endogenous and exogenous NO on the Ca(2+) sparks through ryanodine-sensitive channels in the sarcoplasmic reticulum of an intact artery. Calcium sparks, detected with fluo-4 and laser scanning confocal microscopy, were examined in isolated pressurized rat posterior cerebral arteries with (intact) and without endothelium (denuded).