Cl⁻ channels in smooth muscle cells

Properties of synchronous spontaneous Ca2+ transients in the mural cells of rat rectal arterioles

Synchrony of spontaneous Ca²⁺ transients among venular mural cells (smooth muscle cells and pericytes) in visceral organs relies on the intercellular spread of L-type voltage-dependent Ca²⁺ channel (LVDCC)-dependent depolarisations. However, the mechanisms underlying the synchrony of spontaneous Ca²⁺ transients between arteriolar mural cells are less understood. The spontaneous intracellular Ca²⁺ dynamics of arteriolar mural cells in the rat rectal submucosa were visualised by Cal-520 Ca²⁺ imaging to analyse their synchrony. The mural cells in fine arterioles that had a rounded cell body with several extended processes developed spontaneous 'synchronous' Ca²⁺ transients arising from Ca²⁺ released from sarcoendoplasmic reticulum Ca²⁺ stores. Gap junction blockers (3 μM carbenoxolone, 10 μM 18β-glycyrrhetinic acid), a Ca²⁺-activated Cl^- channel (CaCC) blocker (100 μM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) or lowering extracellular Cl^- concentration (from 134.4 to 12.4 mM) disrupted the synchrony of Ca²⁺ transients between arteriolar mural cells. Blockers of T-type voltage-dependent Ca²⁺ channels (TVDCCs, 1 μM mibefradil or ML218) or LVDCCs (1 μM nifedipine) reduced the Ca²⁺ transient frequency or their area under curve (AUC), respectively. However, neither TVDCC nor LVDCC blockers disrupted the synchrony of Ca²⁺ transients among arteriolar mural cells. This is in contrast with rectal venules in which nifedipine disrupted the synchrony of spontaneous Ca²⁺ transients. Thus, spontaneous transient depolarisations arising from the opening of CaCCs may effectively spread to neighbouring arteriolar mural cells via gap junctions to maintain the Ca²⁺ transient synchrony. Activation of TVDCCs appears to accelerate spontaneous Ca²⁺ transients, while LVDCCs predominantly contribute to the duration of Ca²⁺ transients.

ANO1 in intramuscular interstitial cells of Cajal plays a key role in the generation of slow waves and tone in the internal anal sphincter

KEY POINTS

The internal anal sphincter develops tone important for maintaining high anal pressure and continence. Controversy exists regarding the mechanisms underlying tone development. We examined the hypothesis that tone depends upon electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca²⁺ -activated Cl^- channels (ANO1, encoded by Ano1) and voltage-dependent L-type Ca²⁺ channels (Cav_L , encoded by Cacna1c). Measurement of membrane potential and contraction indicated that ANO1 and Cav_L have a central role in SW generation, phasic contractions and tone, independent of stretch. ANO1 expression was examined in wildtype and Ano1^/+egfp mice with immunohistochemical techniques. Ano1 and Cacna1c expression levels were examined by quantitative PCR in fluorescence-activated cell sorting. ICC-IM were the predominant cell type expressing ANO1 and the most likely candidate for SW generation. SWs in ICC-IM are proposed to conduct to smooth muscle where Ca²⁺ entry via Cav_L results in phasic activity that sums to produce tone.

ABSTRACT

The mechanism underlying tone generation in the internal anal sphincter (IAS) is controversial. We examined the hypothesis that tone depends upon generation of electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca²⁺ -activated Cl^- channels (encoded by Ano1) and voltage-dependent L-type Ca²⁺ channels (encoded by Cacna1c). Phasic contractions and tone in the IAS were nearly abolished by ANO1 and Cav_L antagonists. ANO1 antagonists also abolished SWs as well as transient depolarizations that persisted after addition of Cav_L antagonists. Tone development in the IAS did not require stretch of muscles, and the sensitivity of contraction to ANO1 antagonists was the same in stretched versus un-stretched muscles. ANO1 expression was examined in wildtype and Ano1^/+egfp mice with immunohistochemical techniques. Dual labelling revealed that ANO1 expression could be resolved in ICC but not smooth muscle cells (SMCs) in the IAS and rectum. Ano1, Cacna1c and Kit gene expression were the same in extracts of IAS and rectum muscles. In IAS cells isolated with fluorescence-activated cell sorting, Ano1 expression was 26.5-fold greater in ICC than in SMCs while Cacna1c expression was only 2-fold greater in SMCs than in ICC. These data support a central role for ANO1 and Cav_L in the generation of SWs and tone in the IAS. ICC-IM are the probable cellular candidate for ANO1 currents and SW generation. We propose that ANO1 and Cav_L collaborate to generate SWs in ICC-IM followed by conduction to adjacent SMCs where phasic calcium entry through Cav_L sums to produce tone.

Negative News: Cl− and HCO3− in the Vascular Wall

Cl− and HCO3− are the most prevalent membrane-permeable anions in the intra- and extracellular spaces of the vascular wall. Outwardly directed electrochemical gradients for Cl− and HCO3− permit anion channel opening to depolarize vascular smooth muscle and endothelial cells. Transporters and channels for Cl− and HCO3− also modify vascular contractility and structure independently of membrane potential. Transport of HCO3− regulates intracellular pH and thereby modifies the activity of enzymes, ion channels, and receptors. There is also evidence that Cl− and HCO3− transport proteins affect gene expression and protein trafficking. Considering the extensive implications of Cl− and HCO3− in the vascular wall, it is critical to understand how these ions are transported under physiological conditions and how disturbances in their transport can contribute to disease development. Recently, sensing mechanisms for Cl− and HCO3− have been identified in the vascular wall where they modify ion transport and vasomotor function, for instance, during metabolic disturbances. This review discusses current evidence that transport (e.g., via NKCC1, NBCn1, Ca2+-activated Cl− channels, volume-regulated anion channels, and CFTR) and sensing (e.g., via WNK and RPTPγ) of Cl− and HCO3− influence cardiovascular health and disease.

Vascular CaMKII: heart and brain in your arteries

First characterized in neuronal tissues, the multifunctional calcium/calmodulin-dependent protein kinase II (CaMKII) is a key signaling component in several mammalian biological systems. Its unique capacity to integrate various Ca(2+) signals into different specific outcomes is a precious asset to excitable and nonexcitable cells. Numerous studies have reported roles and mechanisms involving CaMKII in brain and heart tissues. However, corresponding functions in vascular cell types (endothelium and vascular smooth muscle cells) remained largely unexplored until recently. Investigation of the intracellular Ca(2+) dynamics, their impact on vascular cell function, the regulatory processes involved and more recently the spatially restricted oscillatory Ca(2+) signals and microdomains triggered significant interest towards proteins like CaMKII. Heteromultimerization of CaMKII isoforms (four isoforms and several splice variants) expands this kinase's peculiar capacity to decipher Ca(2+) signals and initiate specific signaling processes, and thus controlling cellular functions. The physiological functions that rely on CaMKII are unsurprisingly diverse, ranging from regulating contractile state and cellular proliferation to Ca(2+) homeostasis and cellular permeability. This review will focus on emerging evidence of CaMKII as an essential component of the vascular system, with a focus on the kinase isoform/splice variants and cellular system studied.

Local coupling of TRPC6 to ANO1/TMEM16A channels in smooth muscle cells amplifies vasoconstriction in cerebral arteries

Anoctamin-1 [ANO1, also known as transmembrane protein 16A (TMEM16A)] is a Ca(2+)-activated Cl(-) channel expressed in arterial myocytes that regulates membrane potential and contractility. Signaling mechanisms that control ANO1 activity in arterial myocytes are poorly understood. In cerebral artery myocytes, ANO1 channels are activated by local Ca(2+) signals generated by plasma membrane nonselective cation channels, but the molecular identity of these proteins is unclear. Arterial myocytes express several different nonselective cation channels, including multiple members of the transient receptor potential receptor (TRP) family. The goal of this study was to identify localized ion channels that control ANO1 currents in cerebral artery myocytes. Coimmunoprecipitation and immunofluorescence resonance energy transfer microscopy experiments indicate that ANO1 and canonical TRP 6 (TRPC6) channels are present in the same macromolecular complex and localize in close spatial proximity in the myocyte plasma membrane. In contrast, ANO1 is not near TRPC3, TRP melastatin 4, or inositol trisphosphate receptor 1 channels. Hyp9, a selective TRPC6 channel activator, stimulated Cl(-) currents in myocytes that were blocked by T16Ainh-A01, an ANO1 inhibitor, ANO1 knockdown using siRNA, and equimolar replacement of intracellular EGTA with BAPTA, a fast Ca(2+) chelator that abolishes local Ca(2+) signaling. Hyp9 constricted pressurized cerebral arteries, and this response was attenuated by T16Ainh-A01. In contrast, T16Ainh-A01 did not alter depolarization-induced (60 mM K(+)) vasoconstriction. These data indicate that TRPC6 channels generate a local intracellular Ca(2+) signal that activates nearby ANO1 channels in myocytes to stimulate vasoconstriction.

The molecular basis of the genesis of basal tone in internal anal sphincter

Smooth muscle sphincters exhibit basal tone and control passage of contents through organs such as the gastrointestinal tract; loss of this tone leads to disorders such as faecal incontinence. However, the molecular mechanisms underlying this tone remain unknown. Here, we show that deletion of myosin light-chain kinases (MLCK) in the smooth muscle cells from internal anal sphincter (IAS-SMCs) abolishes basal tone, impairing defecation. Pharmacological regulation of ryanodine receptors (RyRs), L-type voltage-dependent Ca²⁺ channels (VDCCs) or TMEM16A Ca²⁺-activated Cl⁻ channels significantly changes global cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and the tone. TMEM16A deletion in IAS-SMCs abolishes the effects of modulators for TMEM16A or VDCCs on a RyR-mediated rise in global [Ca²⁺]_i and impairs the tone and defecation. Hence, MLCK activation in IAS-SMCs caused by a global rise in [Ca²⁺]_i via a RyR-TMEM16A-VDCC signalling module sets the basal tone. Targeting this module may lead to new treatments for diseases like faecal incontinence.

The molecular basis of the basal tone generated by internal anal sphincters (IAS) is largely unknown. Here, the authors show that the tone arises from a global rise in intracellular Ca²⁺ in smooth muscle cells via a Ryanodine receptor-TMEM16A-L-type Ca²⁺ channel-MLC kinase pathway, suggesting a potential therapy for IAS motility disorders.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.

Novel regulatory mechanism in human urinary bladder: central role of transient receptor potential melastatin 4 channels in detrusor smooth muscle function

Transient receptor potential melastatin 4 (TRPM4) channels are Ca(2+)-activated nonselective cation channels that have been recently identified as regulators of detrusor smooth muscle (DSM) function in rodents. However, their expression and function in human DSM remain unexplored. We provide insights into the functional role of TRPM4 channels in human DSM under physiological conditions. We used a multidisciplinary experimental approach, including RT-PCR, Western blotting, immunohistochemistry and immunocytochemistry, patch-clamp electrophysiology, and functional studies of DSM contractility. DSM samples were obtained from patients without preoperative overactive bladder symptoms. RT-PCR detected mRNA transcripts for TRPM4 channels in human DSM whole tissue and freshly isolated single cells. Western blotting and immunohistochemistry with confocal microscopy revealed TRPM4 protein expression in human DSM. Immunocytochemistry further detected TRPM4 protein expression in DSM single cells. Patch-clamp experiments showed that 9-phenanthrol, a selective TRPM4 channel inhibitor, significantly decreased the transient inward cation currents and voltage step-induced whole cell currents in freshly isolated human DSM cells. In current-clamp mode, 9-phenanthrol hyperpolarized the human DSM cell membrane potential. Furthermore, 9-phenanthrol attenuated the spontaneous phasic, carbachol-induced and nerve-evoked contractions in human DSM isolated strips. Significant species-related differences in TRPM4 channel activity between human, rat, and guinea pig DSM were revealed, suggesting a more prominent physiological role for the TRPM4 channel in the regulation of DSM function in humans than in rodents. In conclusion, TRPM4 channels regulate human DSM excitability and contractility and are critical determinants of human urinary bladder function. Thus, TRPM4 channels could represent promising novel targets for the pharmacological or genetic control of overactive bladder.

Mechanisms underlying spontaneous constrictions of postcapillary venules in the rat stomach

Postcapillary venules (PCVs) play a critical role in regulating capillary hydrostatic pressure, but their contractile mechanisms are not well understood. We examined the properties of spontaneous vasomotion and corresponding Ca(2+) transients in gastric PCV. In the rat gastric submucosa, changes in PCV diameter and intracellular Ca(2+) dynamics were visualised by video tracking system and fluorescent Ca(2+) imaging, respectively, while PCV morphology was examined by immunohistochemistry. Stellate-shaped PCV mural cells expressing α-smooth muscle actin exhibited synchronised spontaneous Ca(2+) transients to develop vasomotion which was abolished by nifedipine (1 μM), cyclopiazonic acid (10 μM), or Ca(2+)-activated Cl(-) channel inhibitors (100 μM niflumic acid, 1 μM T16Ainh-A01). A gap junction blocker (3 μM carbenoxolone) disrupted the synchrony of spontaneous Ca(2+) transients amongst PCV mural cells and attenuated spontaneous vasomotion. Low chloride solution ([Cl(-)]0 = 12.4 mM) also disrupted the synchrony of spontaneous Ca(2+) transients and abolished vasomotion. Na(+)-K(+)-Cl(-) co-transporter inhibitors (10 μM bumetanide, 30 μM furosemide) suppressed spontaneous Ca(2+) transients and vasoconstrictions. A phosphodiesterase type 5 (PDE5) inhibitor (1 μM tadalafil) disrupted the spontaneous Ca(2+) transient synchrony and abolished vasomotion in a nitric oxide (NO)-dependent manner. Thus, gastric PCVs exhibit spontaneous vasomotion, resulting from synchronised spontaneous Ca(2+) transients within a network of stellate-shaped PCV mural cells. An active Cl(-) accumulation partly via Na(+)-K(+)-Cl(-) co-transport appears to be fundamental in maintaining depolarisation upon the opening of Ca(2+)-activated Cl(-) channels that triggers Ca(2+) influx via voltage-dependent L-type Ca(2+) channels. Basal PDE5 activity may continuously counteract vaso-relaxing effects of endothelial NO to maintain spontaneous vasomotion.

A novel exon in the human Ca2+-activated Cl- channel Ano1 imparts greater sensitivity to intracellular Ca2

Anoctamin 1 (Ano1; TMEM16A) is a Ca(2+)-activated Cl(-) channel (CACC) expressed in interstitial cells of Cajal. The mechanisms by which Ca(2+) regulates Ano1 are incompletely understood. In the gastrointestinal tract, Ano1 is required for normal slow wave activity and is involved in regulating cell proliferation. Splice variants of Ano1 have varying electrophysiological properties and altered expression in disease states. Recently, we identified a transcript for human Ano1 containing a novel exon-"exon 0" upstream of and in frame with exon 1. The electrophysiological properties of this longer Ano1 isoform are unknown. Our aim was to determine the functional contribution of the newly identified exon to the Ca(2+) sensitivity and electrophysiological properties of Ano1. Constructs with [Ano1(+0)] or without [Ano1(-0)] the newly identified exon were transfected into human embryonic kidney-293 cells. Voltage-clamp electrophysiology was used to determine voltage- and time-dependent parameters of whole cell Cl(-) currents between isoforms with varying concentrations of intracellular Ca(2+), extracellular anions, or Cl(-) channel inhibitors. We found that exon 0 did not change voltage sensitivity and had no impact on the relative permeability of Ano1 to most anions. Ano1(+0) exhibited greater changes in current density but lesser changes in kinetics than Ano1(-0) in response to varying intracellular Ca(2+). The CACC inhibitor niflumic acid inhibited current with greater efficacy and higher potency against Ano1(+0) compared with Ano1(-0). Likewise, the Ano1 inhibitor T16Ainh-A01 reduced Ano1(+0) more than Ano1(-0). In conclusion, human Ano1 containing exon 0 imparts its Cl(-) current with greater sensitivity to intracellular Ca(2+) and CACC inhibitors.

Ion channels of the mammalian urethra

The mammalian urethra is a muscular tube responsible for ensuring that urine remains in the urinary bladder until urination. In order to prevent involuntary urine leakage, the urethral musculature must be capable of constricting the urethral lumen to an extent that exceeds bladder intravesicular pressure during the urine-filling phase. The main challenge in anti-incontinence treatments involves selectively-controlling the excitability of the smooth muscles in the lower urinary tract. Almost all strategies to battle urinary incontinence involve targeting the bladder and as a result, this tissue has been the focus for the majority of research and development efforts. There is now increasing recognition of the value of targeting the urethral musculature in the treatment and management of urinary incontinence. Newly-identified and characterized ion channels and pathways in the smooth muscle of the urethra provides a range of potential therapeutic targets for the treatment of urinary incontinence. This review provides a summary of the current state of knowledge of the ion channels discovered in urethral smooth muscle cells that regulate their excitability.

The bestrophin- and TMEM16A-associated Ca(2+)- activated Cl(–) channels in vascular smooth muscles

The presence of Ca²⁺-activated Cl^– currents (I_Cl(Ca)) in vascular smooth muscle cells (VSMCs) is well established. I_Cl(Ca) are supposedly important for arterial contraction by linking changes in [Ca²⁺]_i and membrane depolarization. Bestrophins and some members of the TMEM16 protein family were recently associated with I_Cl(Ca). Two distinct I_Cl(Ca) are characterized in VSMCs; the cGMP-dependent I_Cl(Ca) dependent upon bestrophin expression and the ‘classical’ Ca²⁺-activated Cl^– current, which is bestrophin-independent. Interestingly, TMEM16A is essential for both the cGMP-dependent and the classical I_Cl(Ca). Furthermore, TMEM16A has a role in arterial contraction while bestrophins do not. TMEM16A’s role in the contractile response cannot be explained however only by a simple suppression of the depolarization by Cl^– channels. It is suggested that TMEM16A expression modulates voltage-gated Ca²⁺ influx in a voltage-independent manner and recent studies also demonstrate a complex role of TMEM16A in modulating other membrane proteins.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Activation of Ca(2+) -activated Cl(-) channel ANO1 by localized Ca(2+) signals

Ca²⁺‐activated chloride channels (CaCCs) regulate numerous physiological processes including epithelial transport, smooth muscle contraction and sensory processing. Anoctamin‐1 (ANO1, TMEM16A) is a principal CaCC subunit in many cell types, yet our understanding of the mechanisms of ANO1 activation and regulation are only beginning to emerge. Ca²⁺ sensitivity of ANO1 is rather low and at negative membrane potentials the channel requires several micromoles of intracellular Ca²⁺ for activation. However, global Ca²⁺ levels in cells rarely reach such levels and, therefore, there must be mechanisms that focus intracellular Ca²⁺ transients towards the ANO1 channels. Recent findings indeed indicate that ANO1 channels often co‐localize with sources of intracellular Ca²⁺ signals. Interestingly, it appears that in many cell types ANO1 is particularly tightly coupled to the Ca²⁺ release sites of the intracellular Ca²⁺ stores. Such preferential coupling may represent a general mechanism of ANO1 activation in native tissues.

Insulin is involved in transcriptional regulation of NKCC and the CFTR Cl(-) channel through PI3K activation and ERK inactivation in renal epithelial cells

It is is well known that insulin stimulates glucose transport and epithelial Na(+) channel (ENaC)-mediated Na(+) reabsorption; however, the action of insulin on Cl(-) secretion is not fully understood. In this study, we investigated the action of insulin on Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-mediated Cl(-) secretion in epithelial A6 cells. Interestingly, insulin treatment remarkably enhanced the forskolin-stimulated Cl(-) secretion associated with an increase in apical Cl(-) conductance by upregulating mRNA expression of both CFTR and NKCC, although insulin treatment alone had no effect on the basal Cl(-) secretion or apical Cl(-) conductance without forskolin application. We next elucidated a role of phosphoinositide 3-kinase (PI3K) in the insulin-induced enhancement of the Cl(-) secretion, since insulin actually activated PI3K, resulting in activation of Akt, a downstream molecule of PI3K. LY294002 (a PI3K inhibitor) reduced the Cl(-) secretion by suppressing mRNA expression of NKCC, whereas insulin still had a stimulatory action on mRNA expression of CFTR even in the presence of LY294002. On the other hand, we found that a MEK inhibitor (PD98059) further enhanced the insulin-stimulated CFTR mRNA expression and the Cl(-) secretion in forskolin-stimulated A6 cells and that insulin induced slight, transient activation of ERK followed by significant inactivation of ERK. These observations suggest that: (1) insulin respectively upregulates mRNA expression of NKCC and CFTR through activation of PI3K and inactivation of ERK; (2) insulin signals on mRNA expression of NKCC and CFTR are not enough to stimulate transepithelial Cl(-) secretion, but enhance the stimulatory action of cAMP on transepithelial Cl(-) secretion.

Ano1, a Ca2+-activated Cl- channel, coordinates contractility in mouse intestine by Ca2+ transient coordination between interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are pacemaker cells that generate electrical activity to drive contractility in the gastrointestinal tract via ion channels. Ano1 (Tmem16a), a Ca(2+)-activated Cl(-) channel, is an ion channel expressed in ICC. Genetic deletion of Ano1 in mice resulted in loss of slow waves in smooth muscle of small intestine. In this study, we show that Ano1 is required to maintain coordinated Ca(2+) transients between myenteric ICC (ICC-MY) of small intestine. First, we found spontaneous Ca(2+) transients in ICC-MY in both Ano1 WT and knockout (KO) mice. However, Ca(2+) transients within the ICC-MY network in Ano1 KO mice were uncoordinated, while ICC-MY Ca(2+) transients in Ano1 WT mice were rhythmic and coordinated. To confirm the role of Ano1 in the loss of Ca(2+) transient coordination, we used pharmacological inhibitors of Ano1 activity and shRNA-mediated knock down of Ano1 expression in organotypic cultures of Ano1 WT small intestine. Coordinated Ca(2+) transients became uncoordinated using both these approaches, supporting the conclusion that Ano1 is required to maintain coordination/rhythmicity of Ca(2+) transients. We next determined the effect on smooth muscle contractility using spatiotemporal maps of contractile activity in Ano1 KO and WT tissues. Significantly decreased contractility that appeared to be non-rhythmic and uncoordinated was observed in Ano1 KO jejunum. In conclusion, Ano1 has a previously unidentified role in the regulation of coordinated gastrointestinal smooth muscle function through coordination of Ca(2+) transients in ICC-MY.

The TRPM4 channel inhibitor 9-phenanthrol

The phenanthrene-derivative 9-phenanthrol is a recently identified inhibitor of the transient receptor potential melastatin (TRPM) 4 channel, a Ca(2+) -activated non-selective cation channel whose mechanism of action remains to be determined. Subsequent studies performed on other ion channels confirm the specificity of the drug for TRPM4. In addition, 9-phenanthrol modulates a variety of physiological processes through TRPM4 current inhibition and thus exerts beneficial effects in several pathological conditions. 9-Phenanthrol modulates smooth muscle contraction in bladder and cerebral arteries, affects spontaneous activity in neurons and in the heart, and reduces lipopolysaccharide-induced cell death. Among promising potential applications, 9-phenanthrol exerts cardioprotective effects against ischaemia-reperfusion injuries and reduces ischaemic stroke injuries. In addition to reviewing the biophysical effects of 9-phenanthrol, here we present information about its appropriate use in physiological studies and possible clinical applications.