Single-Operator Left atrial appendage Occlusion utilizing Conscious sedation TEE, Lack of Outpatient pre-imaging, and Same-day Expedited discharge (SOLO-CLOSE): A comparison with conventional approach

BACKGROUND

Left atrial appendage occlusion (LAAO) with WATCHMAN currently requires preprocedural imaging, general anesthesia, and inpatient overnight admission. We sought to facilitate simplification of LAAO.

AIMS

We describe and compare SOLO-CLOSE (single-operator LAA occlusion utilizing conscious sedation TEE, lack of outpatient pre-imaging, and same-day expedited discharge) with the conventional approach (CA).

METHODS

A single-center retrospective analysis of 163 patients undergoing LAAO between January 2017 and April 2022 was conducted. The SOLO-CLOSE protocol was enacted on December 1, 2020. Before this date, we utilized the CA. The primary efficacy endpoint was defined as successful LAAO with ≤5 mm peri-device leak at time of closure. The primary safety endpoint was the composite incidence of all-cause deaths, any cerebrovascular accident (CVA), device embolization, pericardial effusion, or major postprocedure bleeding within 7 days of the index procedure. Procedure times, 7-day readmission rates, and cost analytics were collected as well.

RESULTS

Baseline characteristics were similar in both cohorts. Congestive heart failure (37.5% vs. 11.1%) and malignancy (28.8% vs. 12.5%) were higher in SOLO-CLOSE. Median CHA2D2SVASc score was 5 in both cohorts. The primary efficacy endpoint was met 100% in both cohorts. Primary safety endpoint was similar between cohorts (p = 0.078). Mean procedure time was 30 min shorter in SOLO-CLOSE (p < 0.01). Seven-day readmissions for SOLO-CLOSE was zero. After SOLO-CLOSE implementation, there was a 188% increase in positive contribution margin per case.

CONCLUSIONS

The SOLO-CLOSE methodology offers similar efficacy and safety when compared to the CA, while improving clinical efficiency, reducing procedural times, and increasing economic benefit.

Severe aortic insufficiency-induced cardiogenic shock treated with left atrial VA-ECMO and emergent valve-in-valve TAVR

Conventional venoarterial extracorporeal membrane oxygenation (VA-ECMO) places a functional afterload burden on the left ventricle. In the setting of acute severe aortic insufficiency-induced cardiogenic shock, the utility of VA-ECMO in combination with a failing valve may result in catastrophic haemodynamic consequences. This challenge is compounded when the culprit is a failing surgical bioprosthetic valve. We present a case of severe rapid-onset bioprosthetic aortic insufficiency-induced cardiogenic shock successfully resuscitated with left atrial VA-ECMO promptly followed by emergent percutaneous valve-in-valve transaortic valve replacement. We discuss the logistics, implications, and associated haemodynamic manifestations in utilizing this strategy for such disease processes.

Death-associated protein kinase 3 regulates the myogenic reactivity of cerebral arteries

NEW FINDINGS

What is the central question of this study? DAPK3 contributes to the Ca2+ -sensitization of vascular smooth muscle contraction: does this protein kinase participate in the myogenic response of cerebral arteries? What is the main finding and its importance? Small molecule inhibitors of DAPK3 effectively block the myogenic responses of cerebral arteries. HS38-dependent changes to vessel constriction occur independent of LC20 phosphorylation, and therefore DAPK3 appears to operate via the actin cytoskeleton. A role for DAPK3 in the myogenic response was not previously reported, and the results support a potential new therapeutic target in the cerebrovascular system.

ABSTRACT

The vascular smooth muscle (VSM) of resistance blood vessels is a target of intrinsic autoregulatory responses to increased intraluminal pressure, the myogenic response. In the brain, the myogenic reactivity of cerebral arteries is critical to homeostatic blood flow regulation. Here we provide the first evidence to link the death-associated protein kinase 3 (DAPK3) to the myogenic response of rat and human cerebral arteries. DAPK3 is a Ser/Thr kinase involved in Ca2+ -sensitization mechanisms of smooth muscle contraction. Ex vivo administration of a specific DAPK3 inhibitor (i.e., HS38) could attenuate vessel constrictions invoked by serotonin as well as intraluminal pressure elevation. The HS38-dependent dilatation was not associated with any change in myosin light chain (LC20) phosphorylation. The results suggest that DAPK3 does not regulate Ca2+ sensitization pathways during the myogenic response of cerebral vessels but rather operates to control the actin cytoskeleton. A slow return of myogenic tone was observed during the sustained ex vivo exposure of cerebral arteries to HS38. Recovery of tone was associated with greater LC20 phosphorylation that suggests intrinsic signalling compensation in response to attenuation of DAPK3 activity. Additional experiments with VSM cells revealed HS38- and siDAPK-dependent effects on the actin cytoskeleton and focal adhesion kinase phosphorylation status. The translational importance of DAPK3 to the human cerebral vasculature was noted, with robust expression of the protein kinase and significant HS38-dependent attenuation of myogenic reactivity found for human pial vessels.

Smoothelin-like 1 knockout mice display sex-dependent alterations in blood flow and cardiac function

Smoothelin-like 1 (SMTNL1) modulates the contractile performance of smooth muscle and thus has a key role in vascular homeostasis. Elevated vascular tone, recognized as a contributor to the development of progressive cardiac dysfunction, was previously found with SMTNL1 deletion. In this study, we assessed cardiac morphology and function of male and female, wild-type (Smtnl1^+/+) and global SMTNL1 knockout (Smtnl1^-/-) mice at 10 weeks of age. Gross dissection revealed distinct cardiac morphology only in males; Smtnl1^-/- hearts were significantly smaller than Smtnl1^+/+, but the left ventricle (LV) proportion of heart mass was greater. Male Smtnl1^-/- mice also displayed increased ejection fraction and fractional shortening, as well as elevated aortic and pulmonary flow velocities. The impact of cardiac stress with pressure overload by transverse aortic constriction (TAC) was examined in male mice. With TAC banding, systolic function was preserved, but the LV filling pressure was selectively elevated due to relaxation impairment. Smtnl1^-/- mice displayed higher early/passive filling velocity of LV/early mitral annulus velocity ratio (E/E' ratio) and myocardial performance index along with a prolonged isovolumetric relaxation time. Taken together, the findings support a novel, sex-dimorphic role for SMTNL1 in modulating cardiac structure and function of mice.

Amniotic fluid embolism‐induced cardiopulmonary collapse successfully treated with combination VA‐ECMO and Impella CP

Amniotic fluid embolism (AFE) is a rare but potentially fatal complication of pregnancy. Prompt and aggressive resuscitative strategies are crucial in promoting survivability. We present a case of AFE resulting in cardiopulmonary collapse and subsequent cardiac arrest where we were able to safely deliver the baby and resuscitate the mother with veno-arterial extracorporeal membrane oxygenation and Impella CP-a novel combination known as ECPELLA. We discuss the implications of this approach as a more efficacious strategy in resuscitating AFE-induced cardiogenic shock and arrest.

Prenatal exposure to a low dose of BPS causes sex-dependent alterations to vascular endothelial function in adult offspring

Background: Bisphenol S (BPS) is among the most commonly used substitutes for Bisphenol A (BPA), an endocrine disrupting chemical used as a plasticizer in the manufacture of polycarbonate plastics and epoxy resins. Bisphenols interfere with estrogen receptor (ER) signaling, which modulates vascular function through stimulation of nitric oxide (NO) production via endothelial nitric oxide synthase (eNOS). BPS can cross into the placenta and accumulates in the fetal compartment to a greater extent than BPA, potentially interfering with key developmental events. Little is known regarding the developmental impact of exposure to BPA substitutes, particularly with respect to the vasculature.

Objective: To determine if prenatal BPS exposure influences vascular health in adulthood.

Methods: At the time of mating, female C57BL/6 dams were administered BPS (250 nM) or vehicle control in the drinking water, and exposure continued during lactation. At 12-week of age, mesenteric arteries were excised from male and female offspring and assessed for responses to an endothelium-dependent (acetylcholine, ACh) and endothelium-independent (sodium nitroprusside, SNP) vasodilator. Endothelium-dependent dilation was measured in the presence or absence of L-NAME, an eNOS inhibitor. To further explore the role of NO and ER signaling, wire myography was used to assess ACh responses in aortic rings after acute exposure to BPS in the presence or absence of L-NAME or an ER antagonist.

Results: Increased ACh dilation and increased sensitivity to Phe were observed in microvessels from BPS-exposed females, while no changes were observed in male offspring. Differences in ACh-induced dilation between control or BPS-exposed females were eliminated with L-NAME. Increased dilatory responses to ACh after acute BPS exposure were observed in aortic rings from female mice only, and differences were eliminated with inhibition of eNOS or inhibition of ER.

Conclusion: Prenatal BPS exposure leads to persistent changes in endothelium-dependent vascular function in a sex-specific manner that appears to be modulated by interaction of BPS with ER signaling.

Abstract 244: Post- But Not Pre-menopausal Female Smoothelin-like 1 Deficient Mice Develop Diastolic Dysfunction Unlike Their Male Counterparts

Diastolic dysfunction is a core characteristic of heart failure with preserved ejection fraction (HFpEF), which accounts for half of all HF cases. Our group revealed a novel impact of the smoothelin-like 1 (SMTNL1) protein which when subjected to genetic deletion drives alterations in endothelial and cardiovascular performances. Of note, previous cardiac hemodynamic profiling showed that young male SMTNL1 knockout (KO) mice developed diastolic dysfunction as evidenced by increased end diastolic pressure (EDP), left ventricular relaxation time constant (Tau) and steeper end diastolic pressure-volume relationship (EDPVR).

A majority of HFpEF patients are post-menopausal women, so this study examined the impact of SMTNL1 silencing on endothelial and cardiac function with increasing age in a novel female murine model. The cardiac function of SMTNL1 global KO mice (3-, 12- and 18-month old, male and female) was assessed by echocardiography and pressure-volume loop. Unlike young males, 3-month old female KO mice did not develop diastolic dysfunction. However, ageing provided progressive impairment of diastolic function in female KO mice with increased EDP (8.4±1.1 vs 12.2±0.8 mmHg, p<0.02) and EDPVR (0.22±0.05 vs 0.51±0.05, p=0.02) at 18 months; an elevated E/E′ (20.8±1.6 vs 28.3±2.2, p=0.02) and decreased E′/A′ (1.49±0.19 vs 0.97±0.14, p<0.05) at 12 months in comparison to their WT counterparts, along with a normal ejection fraction (>60%) for all age groups. Furthermore, while flow-mediated dilation was continuously impaired in male KO cohorts from 3-month age, female KO showed impairment only at 12-months. Aging was also associated with altered cardiac morphology and fibrotic levels in the aged female KO cohort.

Taken together, we have identified pathophysiologic effects of SMTNL1 silencing on vascular and cardiac function with ageing in female mice. The SMTNL1 KO model for the first time recapitulates the sex dimorphic onset of diastolic dysfunction that is central to HFpEF clinical phenotypes and represents a novel preclinical model to study the etiology of the HFpEF condition. Furthermore, the absence of diastolic dysfunction in KO female mice until post-menopausal age reveals a protective role of female sex hormones and warrants further study.

Normalized Competitive Index: Analyzing Trends in Surgical Fellowship Training Over the Past Decade (2009-2018)

OBJECTIVE

There is a lack of literature describing how competitive surgical fellowships are, especially across specialties. Such information would be valuable to prospective candidates, especially as immediate postresidency subspecialty training becomes the norm for general surgery. Match-rates alone may be misleading indicators as programs may not fill positions with unqualified applicants. We propose a simple metric to analyze the competitiveness of various surgical subspecialties to each other and themselves over time.

DESIGN

Retrospective cohort study. The Competitive Index is defined as the percentage of filled programs within each specialty divided by the match-rate for that specialty. For ease of comparison, a Normalized Competitive Index (NCI) was developed, normalizing the metric for all specialties in that year to a value of 1.

SETTING

The National Resident Matching Program, The Fellowship Council, and the San Francisco Match publicly available match data from 2009 to 2018.

PARTICIPANTS

General Surgery Associated Fellowship Applicants (Abdominal Transplant, Colorectal, Surgical Oncology, Minimally Invasive Surgery, Pediatric, Plastic, Critical Care, Thoracic, and Vascular).

RESULTS

The overall match rate for all specialties was 74.6% and 84.0% of all programs were filled. Over the past decade, pediatric surgery was significantly more competitive than other specialties (NCI 1.67, p < 0.0001), while surgical critical care (NCI 0.58, p < 0.0001) and vascular (NCI 0.90, p < 0.0492) were significantly less competitive. When comparing the NCI within each specialty from the first 5 years (2009-2013) to the last 5 years, (2014-2018), surgical critical care (NCI 0.54 vs. 0.62, p = 0.0462) and thoracic (NCI 0.74 vs. 1.08, p=0.0025) became significantly more competitive, while transplant (NCI 1.10 vs. 0.92, p = 0.0343) and colorectal (NCI 1.32 vs. 1.09, p = 0.0021) became significantly less competitive.

CONCLUSION

The NCI is a metric which might be useful to prospective applicants and which could be provided annually by organizations sponsoring fellowship matching processes. Further research must be performed to establish what defines a qualified applicant in each specialty.

Cyclooxygenase inhibitors for treating preterm labour: What is the molecular evidence? 1

Preterm birth (<37 weeks of gestation) significantly increases the risk of neonatal mortality and morbidity. As many as half of all preterm births occur following spontaneous preterm labour. Since in such cases there are no known reasons for the initiation of labour, treatment of preterm labour (tocolysis) has sought to stop labour contractions and delay delivery. Despite some success, the use of cyclooxygenase (COX) inhibitors is associated with maternal/fetal side effects, and possibly increased risk of preterm birth. Clinical use of these drugs predates the collection of molecular and biochemical evidence in vitro, examining the expression and activity of COX enzymes in pregnant uterine tissues with and without labour. Such evidence is important to the rationale that COX enzymes are, or are not, appropriate targets for the tocolysis. The current study systematically searched existing scientific evidence to address the hypothesis that COX expression/activity is increased with the onset of human labour, in an effort to determine whether there is a rationale for the use of COX inhibitors as tocolytics. Our review identified 44 studies, but determined that there is insufficient evidence to support or refute a role of COX-1/-2 in the onset of preterm labour that supports COX-targeted tocolysis.

Airway epithelial compression promotes airway smooth muscle proliferation and contraction

During acute bronchoconstriction, the airway epithelium becomes mechanically compressed, as airway smooth muscle contracts and the airway narrows. This mechanical compression activates airway epithelium to promote asthmatic airway remodeling. However, whether compressed airway epithelium can feed back on the cause of bronchoconstriction has remained an open question. Here we examine the potential for epithelial compression to augment proliferation and contraction of airway smooth muscle, and thus potentiate further bronchoconstriction and epithelial compression. Well-differentiated primary human bronchial epithelial (HBE) cells maintained in air-liquid interface culture were mechanically compressed to mimic the effect of bronchoconstriction. Primary human airway smooth muscle (HASM) cells were incubated with conditioned media collected from mechanically compressed HBE cells to examine the effect of epithelial-derived mediators on HASM cell proliferation using an EdU assay and HASM cell contraction using traction microscopy. An endothelin receptor antagonist, PD-145065, was employed to probe the role of HBE cell-derived endothelin-1 on the proliferation and contraction of HASM cells. Conditioned media from compressed HBE cells increased HASM cell proliferation, independent of the endothelin-1 signaling pathway. However, conditioned media from compressed HBE cells significantly increased HASM cell basal contraction and histamine-induced contraction, both of which depended on the endothelin-1 signaling pathway. Our data demonstrate that mechanical compression of bronchial epithelial cells contributes to proliferation and basal contraction of airway smooth muscle cells and that augmented contraction depends on epithelial cell-derived endothelin-1. By means of both airway smooth muscle remodeling and contractility, our findings suggest a causal role of epithelial compression on asthma pathogenesis.

The pro-inflammatory cytokine TNF-α inhibits lymphatic pumping via activation of the NF-κB-iNOS signaling pathway

OBJECTIVE

Mesenteric lymphatic vessel pumping, important to propel lymph and immune cells from the intestinal interstitium to the mesenteric lymph nodes, is compromised during intestinal inflammation. The objective of this study was to test the hypothesis that the pro-inflammatory cytokine TNF-α, is a significant contributor to the inflammation-induced lymphatic contractile dysfunction, and to determine its mode of action.

METHODS

Contractile parameters were obtained from isolated rat mesenteric lymphatic vessels mounted on a pressure myograph after 24-hours incubation with or without TNF-α. Various inhibitors were administered, and quantitative real-time PCR, Western blotting, and immunofluorescence confocal imaging were applied to characterize the mechanisms involved in TNF-α actions.

RESULTS

Vessel contraction frequency was significantly decreased after TNF-α treatment and could be restored by selective inhibition of NF-кB, iNOS, guanylate cyclase, and ATP-sensitive K⁺ channels. We further demonstrated that NF-кB inhibition also suppressed the significant increase in iNOS mRNA observed in TNF-α-treated lymphatic vessels and that TNF-α treatment favored the nuclear translocation of the p65 NF-κB subunit.

CONCLUSIONS

These findings suggest that TNF-α decreases mesenteric lymphatic contractility by activating the NF-κB-iNOS signaling pathway. This mechanism could contribute to the alteration of lymphatic pumping reported in intestinal inflammation.

Transient stretch induces cytoskeletal fluidization through the severing action of cofilin

With every deep inspiration (DI) or sigh, the airway wall stretches, as do the airway smooth muscle cells in the airway wall. In response, the airway smooth muscle cell undergoes rapid stretch-induced cytoskeletal fluidization. As a molecular mechanism underlying the cytoskeletal fluidization response, we demonstrate a key role for the actin-severing protein cofilin. Using primary human airway smooth muscle cells, we simulated a DI by imposing a transient stretch of physiological magnitude and duration. We used traction microscopy to measure the resulting changes in contractile forces. After a transient stretch, cofilin-knockdown cells exhibited a 29 ± 5% decrease in contractile force compared with prestretch conditions. By contrast, control cells exhibited a 67 ± 6% decrease ( P < 0.05, knockdown vs. control). Consistent with these contractile force changes with transient stretch, actin filaments in cofilin-knockdown cells remained largely intact, whereas actin filaments in control cells were rapidly disrupted. Furthermore, in cofilin-knockdown cells, contractile force at baseline was higher and rate of remodeling poststretch was slower than in control cells. Additionally, the severing action of cofilin was restricted to the release phase of the transient stretch. We conclude that the actin-severing activity of cofilin is an important factor in stretch-induced cytoskeletal fluidization and may account for an appreciable part of the bronchodilatory effects of a DI.

Abnormal myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization contribute to impaired myogenic regulation of cerebral arterial diameter in the type 2 diabetic Goto-Kakizaki rat

The myogenic response of cerebral resistance arterial smooth muscle to intraluminal pressure elevation is a key physiological mechanism regulating blood flow to the brain. Rho-associated kinase plays a critical role in the myogenic response by activating Ca²⁺ sensitization mechanisms: (i) Rho-associated kinase inhibits myosin light chain phosphatase by phosphorylating its targeting subunit myosin phosphatase targeting subunit 1 (at T855), augmenting 20 kDa myosin regulatory light chain (LC₂₀) phosphorylation and force generation; and (ii) Rho-associated kinase stimulates cytoskeletal actin polymerization, enhancing force transmission to the cell membrane. Here, we tested the hypothesis that abnormal Rho-associated kinase-mediated myosin light chain phosphatase regulation underlies the dysfunctional cerebral myogenic response of the Goto-Kakizaki rat model of type 2 diabetes. Basal levels of myogenic tone, LC₂₀, and MYPT1-T855 phosphorylation were elevated and G-actin content was reduced in arteries of pre-diabetic 8-10 weeks Goto-Kakizaki rats with normal serum insulin and glucose levels. Pressure-dependent myogenic constriction, LC₂₀, and myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization were suppressed in both pre-diabetic Goto-Kakizaki and diabetic (18-20 weeks) Goto-Kakizaki rats, whereas RhoA, ROK2, and MYPT1 expression were unaffected. We conclude that abnormal Rho-associated kinase-mediated Ca²⁺ sensitization contributes to the dysfunctional cerebral myogenic response in the Goto-Kakizaki model of type 2 diabetes.

Health Risks of Low Dose Ionizing Radiation in Humans: A Review

Radiobiologists have been struggling to estimate the health risks from low doses of radiation in humans for decades. Health risks involve not only neoplastic diseases but also somatic mutations that may contribute to other illnesses (including birth defects and ocular maladies) and heritable mutations that may increase the risk of diseases in future generations. Low dose radiation-induced cancer in humans depends on several variables, and most of these variables are not possible to correct for in any epidemiologic study. Some of the confounding factors include (i) interaction of radiation with other physical (UV light), chemical, and biological mutagens and carcinogens in a synergistic manner; (ii) variation in repair mechanisms that depend on dose; (iii) variation in sensitivity of bystander cells to subsequent radiation exposure that depends on whether they have been pre- or postirradiated; and (iv) variation in adaptive response that depends on radiation doses and protective substances (antioxidants). In our opinion, both the linear no-threshold-response and the threshold-response models might not be suitable in predicting cancer risk at low radiation doses in a quantitative sense. Low doses of ionizing radiation should not be considered insignificant for risks of somatic and heritable, mutations and neoplastic and nonneoplastic diseases in humans.

α5-Integrin-mediated cellular signaling contributes to the myogenic response of cerebral resistance arteries

The myogenic response of resistance arterioles and small arteries involving constriction in response to intraluminal pressure elevation and dilation on pressure reduction is fundamental to local blood flow regulation in the microcirculation. Integrins have garnered considerable attention in the context of initiating the myogenic response, but evidence indicative of mechanotransduction by integrin adhesions, for example established changes in tyrosine phosphorylation of key adhesion proteins, has not been obtained to substantiate this interpretation. Here, we evaluated the role of integrin adhesions and associated cellular signaling in the rat cerebral arterial myogenic response using function-blocking antibodies against α5β1-integrins, pharmacological inhibitors of focal adhesion kinase (FAK) and Src family kinase (SFK), an ultra-high-sensitivity western blotting technique, site-specific phosphoprotein antibodies to quantify adhesion and contractile filament protein phosphorylation, and differential centrifugation to determine G-actin levels in rat cerebral arteries at varied intraluminal pressures. Pressure-dependent increases in the levels of phosphorylation of FAK (FAK-Y397, Y576/Y577), SFK (SFK-Y416; Y527 phosphorylation was reduced), vinculin-Y1065, paxillin-Y118 and phosphoinositide-specific phospholipase C-γ1 (PLCγ1)-Y783 were detected. Treatment with α5-integrin function-blocking antibodies, FAK inhibitor FI-14 or SFK inhibitor SU6656 suppressed the changes in adhesion protein phosphorylation, and prevented pressure-dependent phosphorylation of the myosin targeting subunit of myosin light chain phosphatase (MYPT1) at T855 and 20kDa myosin regulatory light chains (LC20) at S19, as well as actin polymerization that are necessary for myogenic constriction. We conclude that mechanotransduction by integrin adhesions and subsequent cellular signaling play a fundamental role in the cerebral arterial myogenic response.

Abnormal Rho-associated kinase activity contributes to the dysfunctional myogenic response of cerebral arteries in type 2 diabetes

The structural and functional integrity of the brain, and therefore, cognition, are critically dependent on the appropriate control of blood flow within the cerebral circulation. Inadequate flow leads to ischemia, whereas excessive flow causes small vessel rupture and (or) blood-brain-barrier disruption. Cerebral blood flow is controlled through the interplay of several physiological mechanisms that regulate the contractile state of vascular smooth muscle cells (VSMCs) within the walls of cerebral resistance arteries and arterioles. The myogenic response of cerebral VSMCs is a key mechanism that is responsible for maintaining constant blood flow during variations in systemic pressure, i.e., flow autoregulation. Inappropriate myogenic control of cerebral blood flow is associated with, and prognostic of, neurological deterioration and poor outcome in patients with several conditions, including type 2 diabetes. Here, we review recent advances in our understanding of the role of inappropriate Rho-associated kinase activity as a cause of impaired myogenic regulation of cerebral arterial diameter in type 2 diabetes.

Cytoskeletal reorganization evoked by Rho-associated kinase- and protein kinase C-catalyzed phosphorylation of cofilin and heat shock protein 27, respectively, contributes to myogenic constriction of rat cerebral arteries

Our understanding of the molecular events contributing to myogenic control of diameter in cerebral resistance arteries in response to changes in intravascular pressure, a fundamental mechanism regulating blood flow to the brain, is incomplete. Myosin light chain kinase and phosphatase activities are known to be increased and decreased, respectively, to augment phosphorylation of the 20-kDa regulatory light chain subunits (LC20) of myosin II, which permits cross-bridge cycling and force development. Here, we assessed the contribution of dynamic reorganization of the actin cytoskeleton and thin filament regulation to the myogenic response and serotonin-evoked constriction of pressurized rat middle cerebral arteries. Arterial diameter and the levels of phosphorylated LC(20), calponin, caldesmon, cofilin, and HSP27, as well as G-actin content, were determined. A decline in G-actin content was observed following pressurization from 10 mm Hg to between 40 and 120 mm Hg and in three conditions in which myogenic or agonist-evoked constriction occurred in the absence of a detectable change in LC20 phosphorylation. No changes in thin filament protein phosphorylation were evident. Pressurization reduced G-actin content and elevated the levels of cofilin and HSP27 phosphorylation. Inhibitors of Rho-associated kinase and PKC prevented the decline in G-actin; reduced cofilin and HSP27 phosphoprotein content, respectively; and blocked the myogenic response. Furthermore, phosphorylation modulators of HSP27 and cofilin induced significant changes in arterial diameter and G-actin content of myogenically active arteries. Taken together, our findings suggest that dynamic reorganization of the cytoskeleton involving increased actin polymerization in response to Rho-associated kinase and PKC signaling contributes significantly to force generation in myogenic constriction of cerebral resistance arteries.

Contribution of kv7.4/kv7.5 heteromers to intrinsic and calcitonin gene-related peptide-induced cerebral reactivity

OBJECTIVE

Middle cerebral artery (MCA) diameter is regulated by inherent myogenic activity and the effect of potent vasodilators such as calcitonin gene-related peptide (CGRP). Previous studies showed that MCAs express KCNQ1, 4, and 5 potassium channel genes, and the expression products (Kv7 channels) participate in the myogenic control of MCA diameter. The present study investigated the contribution of Kv7.4 and Kv7.5 isoforms to myogenic and CGRP regulation of MCA diameter and determined whether they were affected in hypertensive animals.

APPROACH AND RESULTS

Isometric tension recordings performed on MCA from normotensive rats produced CGRP vasodilations that were inhibited by the pan-Kv7 channel blocker linopirdine (P<0.01) and after transfection of arteries with siRNA against KCNQ4 (P<0.01) but not KCNQ5. However, isobaric myography revealed that myogenic constriction in response to increases in intravascular pressure (20-80 mm Hg) was affected by both KCNQ4 and KCNQ5 siRNA. Proximity ligation assay signals were equally abundant for Kv7.4/Kv7.4 or Kv7.4/Kv7.5 antibody combinations but minimal for Kv7.5/Kv7.5 antibodies or Kv7.4/7.1 combinations. In contrast to systemic arteries, Kv7 function and Kv7.4 abundance in MCA were not altered in hypertensive rats.

CONCLUSIONS

This study reveals, for the first time to our knowledge, that in cerebral arteries, Kv7.4 and Kv7.5 proteins exist predominantly as a functional heterotetramer, which regulates intrinsic myogenicity and vasodilation attributed to CGRP. Surprisingly, unlike systemic arteries, Kv7 activity in MCAs is not affected by the development of hypertension, and CGRP-mediated vasodilation is well maintained. As such, cerebrovascular Kv7 channels could be amenable for therapeutic targeting in conditions such as cerebral vasospasm.

Overactive bladder mediated by accelerated Ca2+ influx mode of Na+/Ca2+ exchanger in smooth muscle

The Na(+)/Ca(2+) exchanger (NCX) is thought to be a key molecule in the regulation of cytosolic Ca(2+) dynamics. The relative importance of the two Ca(2+) transport modes of NCX activity leading to Ca(2+) efflux (forward) and influx (reverse) in smooth muscle, however, remains unclear. Unexpectedly, spontaneous contractions of urinary bladder smooth muscle (UBSM) were enhanced in transgenic mice overexpressing NCX1.3 (NCX1.3(tg/tg)). The enhanced activity was attenuated by KB-R7943 or SN-6. Whole cell outward NCX current sensitive to KB-R7943 or Ni(2+) was readily detected in UBSM cells from NCX1.3(tg/tg) but not wild-type mice. Spontaneous Ca(2+) transients in myocytes of NCX1.3(tg/tg) were larger and frequently resulted in propagating events and global elevations in cytosolic Ca(2+) concentration. Significantly, NCX1.3(tg/tg) mice exhibited a pattern of more frequent urination of smaller volumes and this phenotype was reversed by oral administration of KB-R7943. On the other hand, KB-R7943 did not improve it in KB-R7943-insensitive (G833C-)NCX1.3(tg/tg) mice. We conclude that NCX1.3 overexpression is associated with abnormal urination owing to enhanced Ca(2+) influx via reverse mode NCX leading to prolonged, propagating spontaneous Ca(2+) release events and a potentiation of spontaneous UBSM contraction. These findings suggest the possibility that NCX is a candidate molecular target for overactive bladder therapy.

Overactive bladder mediated by accelerated Ca2+ influx mode of Na+/Ca2+ exchanger in smooth muscle

The Na(+)/Ca(2+) exchanger (NCX) is thought to be a key molecule in the regulation of cytosolic Ca(2+) dynamics. The relative importance of the two Ca(2+) transport modes of NCX activity leading to Ca(2+) efflux (forward) and influx (reverse) in smooth muscle, however, remains unclear. Unexpectedly, spontaneous contractions of urinary bladder smooth muscle (UBSM) were enhanced in transgenic mice overexpressing NCX1.3 (NCX1.3(tg/tg)). The enhanced activity was attenuated by KB-R7943 or SN-6. Whole cell outward NCX current sensitive to KB-R7943 or Ni(2+) was readily detected in UBSM cells from NCX1.3(tg/tg) but not wild-type mice. Spontaneous Ca(2+) transients in myocytes of NCX1.3(tg/tg) were larger and frequently resulted in propagating events and global elevations in cytosolic Ca(2+) concentration. Significantly, NCX1.3(tg/tg) mice exhibited a pattern of more frequent urination of smaller volumes and this phenotype was reversed by oral administration of KB-R7943. On the other hand, KB-R7943 did not improve it in KB-R7943-insensitive (G833C-)NCX1.3(tg/tg) mice. We conclude that NCX1.3 overexpression is associated with abnormal urination owing to enhanced Ca(2+) influx via reverse mode NCX leading to prolonged, propagating spontaneous Ca(2+) release events and a potentiation of spontaneous UBSM contraction. These findings suggest the possibility that NCX is a candidate molecular target for overactive bladder therapy.

Ca2+ sensitization due to myosin light chain phosphatase inhibition and cytoskeletal reorganization in the myogenic response of skeletal muscle resistance arteries

Abstract  The myogenic response of resistance arteries to intravascular pressure elevation is a fundamental physiological mechanism of crucial importance for blood pressure regulation and organ-specific control of blood flow. The importance of Ca(2+) entry via voltage-gated Ca(2+) channels leading to phosphorylation of the 20 kDa myosin regulatory light chains (LC20) in the myogenic response is well established. Recent studies, however, have suggested a role for Ca(2+) sensitization via activation of the RhoA/Rho-associated kinase (ROK) pathway in the myogenic response. The possibility that enhanced actin polymerization is also involved in myogenic vasoconstriction has been suggested. Here, we have used pressurized resistance arteries from rat gracilis and cremaster skeletal muscles to assess the contribution to myogenic constriction of Ca(2+) sensitization due to: (1) phosphorylation of the myosin targeting subunit of myosin light chain phosphatase (MYPT1) by ROK; (2) phosphorylation of the 17 kDa protein kinase C (PKC)-potentiated protein phosphatase 1 inhibitor protein (CPI-17) by PKC; and (3) dynamic reorganization of the actin cytoskeleton evoked by ROK and PKC. Arterial diameter, MYPT1, CPI-17 and LC20 phosphorylation, and G-actin content were determined at varied intraluminal pressures ± H1152, GF109203X or latrunculin B to suppress ROK, PKC and actin polymerization, respectively. The myogenic response was associated with an increase in MYPT1 and LC20 phosphorylation that was blocked by H1152. No change in phospho-CPI-17 content was detected although the PKC inhibitor, GF109203X, suppressed myogenic constriction. Basal LC20 phosphorylation at 10 mmHg was high at ∼40%, increased to a maximal level of ∼55% at 80 mmHg, and exhibited no additional change on further pressurization to 120 and 140 mmHg. Myogenic constriction at 80 mmHg was associated with a decline in G-actin content by ∼65% that was blocked by inhibition of ROK or PKC. Taken together, our findings indicate that two mechanisms of Ca(2+) sensitization (ROK-mediated phosphorylation of MYPT1-T855 with augmentation of LC20 phosphorylation, and a ROK- and PKC-evoked increase in actin polymerization) contribute to force generation in the myogenic response of skeletal muscle arterioles.

Reduced KCNQ4-encoded voltage-dependent potassium channel activity underlies impaired β-adrenoceptor-mediated relaxation of renal arteries in hypertension

KCNQ4-encoded voltage-dependent potassium (Kv7.4) channels are important regulators of vascular tone that are severely compromised in models of hypertension. However, there is no information as to the role of these channels in responses to endogenous vasodilators. We used a molecular knockdown strategy, as well as pharmacological tools, to examine the hypothesis that Kv7.4 channels contribute to β-adrenoceptor-mediated vasodilation in the renal vasculature and underlie the vascular deficit in spontaneously hypertensive rats. Quantitative PCR and immunohistochemistry confirmed gene and protein expression of KCNQ1, KCNQ3, KCNQ4, KCNQ5, and Kv7.1, Kv7.4, and Kv7.5 in rat renal artery. Isoproterenol produced concentration-dependent relaxation of precontracted renal arteries and increased Kv7 channel currents in isolated smooth muscle cells. Application of the Kv7 blocker linopirdine attenuated isoproterenol-induced relaxation and current. Isoproterenol-induced relaxations were also reduced in arteries incubated with small interference RNAs targeted to KCNQ4 that produced a ≈60% decrease in Kv7.4 protein level. Relaxation to isoproterenol and the Kv7 activator S-1 were abolished in arteries from spontaneously hypertensive rats, which was associated with ≈60% decrease in Kv7.4 abundance. This study provides the first evidence that Kv7 channels contribute to β-adrenoceptor-mediated vasodilation in the renal vasculature and that abrogation of Kv7.4 channels is strongly implicated in the impaired β-adrenoceptor pathway in spontaneously hypertensive rats. These findings may provide a novel pathogenic link between arterial dysfunction and hypertension.

Antioxidant micronutrient impact on hearing disorders: concept, rationale, and evidence

PURPOSE

Although auditory disorders are complex conditions, device-related modalities dominate current treatment. However, dysfunction from the central cortex to the inner ear apparatus is increasingly thought to be related to biochemical pathway abnormalities and to free radical-induced oxidative damage and chronic inflammation. Therefore, considering appropriate biologic therapy as an adjunct to standard care against these damaging factors may provide rational expansion of treatment options for otolaryngologists and audiologists.

METHODS

This review outlines the biologic concepts related to some auditory and vestibular conditions and details the current rationale for utilizing antioxidants for a spectrum of hearing disorders. The strategy is based on the authors' collective experience in antioxidant science and supported with published research, pilot animal data and preliminary clinical observations.

RESULTS

A comprehensive micronutrient approach was developed to exploit these pathways, and demonstrated safety and efficacy against oxidative damage and inflammation and clinically relevant neuroprotection. Cooperative research with Department of Defense institutions used prospective, randomized designs to show (1) reduction in oxidative damage measured in plasma and urine over six months, (2) protection against oxidative damage during 12 weeks of intense military training, (3) protection against inflammation after total body blast exposure (rodents), (4) strong neuroprotection against chemically-induced Parkinson's disease (rodents), (5) nerve VIII function improvement after concussive head injury in military personnel, and (6) tinnitus improvement in majority of patients after 90-day evaluation.

CONCLUSION

This systematic review of biologic strategies against hearing disorders combined with new animal and human observations may provide a rational basis for expanding current practice paradigms.

Stromatoxin-sensitive, heteromultimeric Kv2.1/Kv9.3 channels contribute to myogenic control of cerebral arterial diameter

Cerebral vascular smooth muscle contractility plays a crucial role in controlling arterial diameter and, thereby, blood flow regulation in the brain. A number of K(+) channels have been suggested to contribute to the regulation of diameter by controlling smooth muscle membrane potential (E(m)) and Ca(2+) influx. Previous studies indicate that stromatoxin (ScTx1)-sensitive, Kv2-containing channels contribute to the control of cerebral arterial diameter at 80 mmHg, but their precise role and molecular composition were not determined. Here, we tested if Kv2 subunits associate with 'silent' subunits from the Kv5, Kv6, Kv8 or Kv9 subfamilies to form heterotetrameric channels that contribute to control of diameter of rat middle cerebral arteries (RMCAs) over a range of intraluminal pressure from 10 to 100 mmHg. The predominant mRNAs expressed by RMCAs encode Kv2.1 and Kv9.3 subunits. Co-localization of Kv2.1 and Kv9.3 proteins at the plasma membrane of dissociated single RMCA myocytes was detected by proximity ligation assay. ScTx1-sensitive native current of RMCA myocytes and Kv2.1/Kv9.3 currents exhibited functional identity based on the similarity of their deactivation kinetics and voltage dependence of activation that were distinct from those of homomultimeric Kv2.1 channels. ScTx1 treatment enhanced the myogenic response of pressurized RMCAs between 40 and 100 mmHg, but this toxin also caused constriction between 10 and 40 mmHg that was not previously observed following inhibition of large conductance Ca(2+)-activated K(+) (BK(Ca)) and Kv1 channels. Taken together, this study defines the molecular basis of Kv2-containing channels and contributes to our understanding of the functional significance of their expression in cerebral vasculature. Specifically, our findings provide the first evidence of heteromultimeric Kv2.1/Kv9.3 channel expression in RMCA myocytes and their distinct contribution to control of cerebral arterial diameter over a wider range of E(m) and transmural pressure than Kv1 or BK(Ca) channels owing to their negative range of voltage-dependent activation.

Rho-associated kinase plays a role in rabbit urethral smooth muscle contraction, but not via enhanced myosin light chain phosphorylation

The involvement of Rho-associated kinase (ROK) in activation of rabbit urethral smooth muscle contraction was investigated by examining the effects of two structurally distinct inhibitors of ROK, Y27632 and H1152, on the contractile response to electric field stimulation, membrane depolarization with KCl, and α1-adrenoceptor stimulation with phenylephrine. Both compounds inhibited contractions elicited by all three stimuli. The protein kinase C inhibitor GF109203X, on the other hand, had no effect. Urethral smooth muscle strips were analyzed for phosphorylation of three potential direct or indirect substrates of ROK: 1) myosin regulatory light chains (LC20) at S19, 2) the myosin-targeting subunit of myosin light chain phosphatase (MYPT1) at T697 and T855, and 3) cofilin at S3. The following results were obtained: 1) under resting tension, LC20 was phosphorylated to 0.65±0.02 mol Pi/mol LC20 (n=21) at S19; 2) LC20 phosphorylation did not change in response to KCl or phenylephrine; 3) ROK inhibition had no effect on LC20 phosphorylation in the absence or presence of contractile stimuli; 4) under resting conditions, MYPT1 was partially phosphorylated at T697 and T855 and cofilin at S3; 5) phosphorylation of MYPT1 and cofilin was unaffected by KCl or phenylephrine; and 6) KCl- and phenylephrine-induced contraction-relaxation cycles did not correlate with actin polymerization-depolymerization. We conclude that ROK plays an important role in urethral smooth muscle contraction, but not via inhibition of MLCP or polymerization of actin.

Participation of KCNQ (Kv7) potassium channels in myogenic control of cerebral arterial diameter

KCNQ gene expression was previously shown in various rodent blood vessels, where the products of KCNQ4 and KCNQ5, Kv7.4 and Kv7.5 potassium channel subunits, respectively, have an influence on vascular reactivity. The aim of this study was to determine if small cerebral resistance arteries of the rat express KCNQ genes and whether Kv7 channels participate in the regulation of myogenic control of diameter. Quantitative reverse transcription polymerase chain reaction (QPCR) was undertaken using RNA isolated from rat middle cerebral arteries (RMCAs) and immunocytochemistry was performed using Kv7 subunit-specific antibodies and freshly isolated RMCA myocytes. KCNQ4 message was more abundant than KCNQ5 = KCNQ1, but KCNQ2 and KCNQ3 message levels were negligible. Kv7.1, Kv7.4 and Kv7.5 immunoreactivity was present at the sarcolemma of freshly isolated RMCA myocytes. Linopirdine (1 microm) partially depressed, whereas the Kv7 activator S-1 (3 and/or 20 microm) enhanced whole-cell Kv7.4 (in HEK 293 cells), as well as native RMCA myocyte Kv current amplitude. The effects of S-1 were voltage-dependent, with progressive loss of stimulation at potentials of >15 mV. At the concentrations employed linopirdine and S-1 did not alter currents due to recombinant Kv1.2/Kv1.5 or Kv2.1/Kv9.3 channels (in HEK 293 cells) that are also expressed by RMCA myocytes. In contrast, another widely used Kv7 blocker, XE991 (10 microm), significantly attenuated native Kv current and also reduced Kv1.2/Kv1.5 and Kv2.1/Kv9.3 currents. Pressurized arterial myography was performed using RMCAs exposed to intravascular pressures of 10-100 mmHg. Linopirdine (1 microm) enhanced the myogenic response at 20 mmHg, whereas the activation of Kv7 channels with S-1 (20 microm) inhibited myogenic constriction at >20 mmHg and reversed the increased myogenic response produced by suppression of Kv2-containing channels with 30 nm stromatoxin (ScTx1). These data reveal a novel contribution of KCNQ gene products to the regulation of myogenic control of cerebral arterial diameter and suggest that Kv7 channel activating drugs may be appropriate candidates for the development of an effective therapy to ameliorate cerebral vasospasm.

Intravascular pressure augments cerebral arterial constriction by inducing voltage-insensitive Ca2+ waves

This study examined whether elevated intravascular pressure stimulates asynchronous Ca(2+) waves in cerebral arterial smooth muscle cells and if their generation contributes to myogenic tone development. The endothelium was removed from rat cerebral arteries, which were then mounted in an arteriograph, pressurized (20-100 mmHg) and examined under a variety of experimental conditions. Diameter and membrane potential (V(M)) were monitored using conventional techniques; Ca(2+) wave generation and myosin light chain (MLC(20))/MYPT1 (myosin phosphatase targeting subunit) phosphorylation were assessed by confocal microscopy and Western blot analysis, respectively. Elevating intravascular pressure increased the proportion of smooth muscle cells firing asynchronous Ca(2+) waves as well as event frequency. Ca(2+) wave augmentation occurred primarily at lower intravascular pressures (<60 mmHg) and ryanodine, a plant alkaloid that depletes the sarcoplasmic reticulum (SR) of Ca(2+), eliminated these events. Ca(2+) wave generation was voltage insensitive as Ca(2+) channel blockade and perturbations in extracellular [K(+)] had little effect on measured parameters. Ryanodine-induced inhibition of Ca(2+) waves attenuated myogenic tone and MLC(20) phosphorylation without altering arterial V(M). Thapsigargin, an SR Ca(2+)-ATPase inhibitor also attenuated Ca(2+) waves, pressure-induced constriction and MLC(20) phosphorylation. The SR-driven component of the myogenic response was proportionally greater at lower intravascular pressures and subsequent MYPT1 phosphorylation measures revealed that SR Ca(2+) waves facilitated pressure-induced MLC(20) phosphorylation through mechanisms that include myosin light chain phosphatase inhibition. Cumulatively, our findings show that mechanical stimuli augment Ca(2+) wave generation in arterial smooth muscle and that these transient events facilitate tone development particularly at lower intravascular pressures by providing a proportion of the Ca(2+) required to directly control MLC(20) phosphorylation.

Pressure-dependent contribution of Rho kinase-mediated calcium sensitization in serotonin-evoked vasoconstriction of rat cerebral arteries

Our understanding of the cellular signalling mechanisms contributing to agonist-induced constriction is almost exclusively based on the study of conduit arteries. Resistance arteries/arterioles have received less attention as standard biochemical approaches lack the necessary sensitivity to permit quantification of phosphoprotein levels in these small vessels. Here, we have employed a novel, highly sensitive Western blotting method to assess: (1) the contribution of Ca(2+) sensitization mediated by phosphorylation of myosin light chain phosphatase targeting subunit 1 (MYPT1) and the 17 kDa PKC-potentiated protein phosphatase 1 inhibitor protein (CPI-17) to serotonin (5-HT)-induced constriction of rat middle cerebral arteries, and (2) whether there is any interplay between pressure-induced myogenic and agonist-induced mechanisms of vasoconstriction. Arterial diameter and levels of MYPT1 (T697 and T855), CPI-17 and 20 kDa myosin light chain subunit (LC(20)) phosphorylation were determined following treatment with 5-HT (1 micromol l(1)) at 10 or 60 mmHg in the absence and presence of H1152 or GF109203X to suppress the activity of Rho-associated kinase (ROK) and protein kinase C (PKC), respectively. Although H1152 and GF109203X suppressed 5-HT-induced constriction and reduced phospho-LC(20) content at 10 mmHg, we failed to detect any increase in MYPT1 or CPI-17 phosphorylation. In contrast, an increase in MYPT1-T697 and MYPT1-T855 phosphorylation, but not phospho-CPI-17 content, was apparent at 60 mmHg following exposure to 5-HT, and the phosphorylation of both MYPT1 sites was sensitive to H1152 inhibition of ROK. The involvement of MYPT1 phosphorylation in the response to 5-HT at 60 mmHg was not dependent on force generation per se, as inhibition of cross-bridge cycling with blebbistatin (10 micromol l(1)) did not affect phosphoprotein content. Taken together, the data indicate that Ca(2+) sensitization owing to ROK-mediated phosphorylation of MYPT1 contributes to 5-HT-evoked vasoconstriction only in the presence of pressure-induced myogenic activation. These findings provide novel evidence of an interplay between myogenic- and agonist-induced vasoconstriction in cerebral resistance arteries.

Identification and functional characterization of protein kinase A-catalyzed phosphorylation of potassium channel Kv1.2 at serine 449

Vascular smooth muscle Kv1 delayed rectifier K+ channels (KDR) containing Kv1.2 control membrane potential and thereby regulate contractility. Vasodilatory agonists acting via protein kinase A (PKA) enhance vascule smooth muscle Kv1 activity, but the molecular basis of this regulation is uncertain. We characterized the role of a C-terminal phosphorylation site, Ser-449, in Kv1.2 expressed in HEK 293 cells by biochemical and electrophysiological methods. We found that 1) in vitro phosphorylation of Kv1.2 occurred exclusively at serine residues, 2) one major phosphopeptide that co-migrated with 449pSASTISK was generated by proteolysis of in vitro phosphorylated Kv1.2, 3) the peptide 445KKSRSASTISK exhibited stoichiometric phosphorylation by PKA in vitro, 4) matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectroscopy (MS) and MS/MS confirmed in vitro Ser-449 phosphorylation by PKA, 5) in situ phosphorylation at Ser-449 was detected in HEK 293 cells by MALDI-TOF MS followed by MS/MS. MIDAS (multiple reaction monitoring-initiated detection and sequencing) analysis revealed additional phosphorylated residues, Ser-440 and Ser-441, 6) in vitro 32P incorporation was significantly reduced in Kv1.2-S449A, Kv1.2-S449D, and Kv1.2-S440A/S441A/S449A mutant channels, but Kv1.2-S440A/S441A was identical to wild-type Kv1.2 (Kv1.2-WT), and 7) bath applied 8-Br-cAMP or dialysis with PKA catalytic subunit (cPKA) increased Kv1.2-WT but not Kv1.2-S449A current amplitude. cPKA increased Kv1.2-WT current in inside-out patches. Rp-CPT-cAMPS reduced Kv1.2-WT current, blocked the increase due to 8-Br-cAMP, but had no effect on Kv1.2-S449A. cPKA increased current due to double mutant Kv1.2-S440A/S441A but had no effect on Kv1.2-S449D or Kv1.2-S440A/S441A/S449A. We conclude that Ser-449 in Kv1.2 is a site of PKA phosphorylation and a potential molecular mechanism for Kv1-containing KDR channel modulation by agonists via PKA activation.

Ca2+ sensitization via phosphorylation of myosin phosphatase targeting subunit at threonine-855 by Rho kinase contributes to the arterial myogenic response

Ca(2+) sensitization has been postulated to contribute to the myogenic contraction of resistance arteries evoked by elevation of transmural pressure. However, the biochemical evidence of pressure-induced increases in phosphorylated myosin light chain phosphatase (MLCP) targeting subunit 1 (MYPT1) and/or 17 kDa protein kinase C (PKC)-potentiated protein phosphatase 1 inhibitor protein (CPI-17) required to sustain this view is not currently available. Here, we determined whether Ca(2+) sensitization pathways involving Rho kinase (ROK)- and PKC-dependent phosphorylation of MYPT1 and CPI-17, respectively, contribute to the myogenic response of rat middle cerebral arteries. ROK inhibitors (Y27632, 0.03-10 micromol l(-1); H1152, 0.001-0.3 micromol l(-1)) and PKC inhibitors (GF109203X, 3 micromol l(-1); Gö6976; 10 micromol l(-1)) suppressed myogenic vasoconstriction between 40 and 120 mmHg. An improved, highly sensitive 3-step Western blot method was developed for detection and quantification of MYPT1 and CPI-17 phosphorylation. Increasing pressure from 10 to 60 or 100 mmHg significantly increased phosphorylation of MYPT1 at threonine-855 (T855) and myosin light chain (LC(20)). Phosphorylation of MYPT1 at threonine-697 (T697) and CPI-17 were not affected by pressure. Pressure-evoked elevations in MYPT1-T855 and LC(20) phosphorylation were reduced by H1152, but MYPT1-T697 phosphorylation was unaffected. Inhibition of PKC with GF109203X did not affect MYPT1 or LC(20) phosphorylation at 100 mmHg. Our findings provide the first direct, biochemical evidence that a Ca(2+) sensitization pathway involving ROK-dependent phosphorylation of MYPT1 at T855 (but not T697) and subsequent augmentation of LC(20) phosphorylation contributes to myogenic control of arterial diameter in the cerebral vasculature. In contrast, suppression of the myogenic response by PKC inhibitors cannot be attributed to block of Ca(2+) sensitization mediated by CPI-17 or MYPT1 phosphorylation.

ATP-sensitive K+ channels in pig urethral smooth muscle cells are heteromultimers of Kir6.1 and Kir6.2

The inwardly rectifying properties and molecular basis of ATP-sensitive K(+) channels (K(ATP) channels) have now been established for several cell types. However, these aspects of nonvascular smooth muscle K(ATP) channels still remain to be defined. In this study, we investigated the molecular basis of the pore of K(ATP) channels of pig urethral smooth muscle cells through a comparative study of the inwardly rectifying properties, conductance, and regulation by PKC of native and homo- and heteroconcatemeric recombinant Kir6.x channels coexpressed with sulfonylurea receptor subunit SUR2B in human embryonic kidney (HEK) 293 cells by the patch-clamp technique (conventional whole-cell and cell-attached modes). In conventional whole-cell clamp recordings, levcromakalim (> or = 1 microM) caused a concentration-dependent increase in current that demonstrated strong inward rectification at positive membrane potentials. In cell-attached mode, the unitary amplitude of levcromakalim-induced native and recombinant heteroconcatemeric Kir6.1-Kir6.2 K(ATP) channels also showed strong inward rectification at positive membrane potentials. Phorbol 12,13-dibutyrate, but not the inactive phorbol ester, 4alpha-phorbol 12,13-didecanoate, enhanced the activity of native and heteroconcatemeric K(ATP) channels at -50 mV. The conductance of the native channels at approximately 43 pS was consistent with that of heteroconcatemeric channels with a pore-forming subunit composition of (Kir6.1)(3)-(Kir6.2). RT-PCR analysis revealed the expression of Kir6.1 and Kir6.2 transcripts in pig urethral myocytes. Our findings provide the first evidence that the predominant K(ATP) channel expressed in pig urethral smooth muscle possesses a unique, heteromeric pore structure that differs from the homomeric Kir6.1 channels of vascular myocytes and is responsible for the differences in inward rectification, conductance, and PKC regulation exhibited by the channels in these smooth muscle cell types.

Homologous regulation of estrogen receptor subtypes in goldfish (Carassius auratus)

While considerable information is available on the physiological effects of estrogen, much less is known about the regulation of estrogen receptor (ER) subtypes, particularly in non-mammalian vertebrates. Using goldfish as primary experimental model, we investigated sex- and tissue-specific homologous regulation of ER subtypes (ERalpha, ERbetaI, and ERbetaII) by estradiol in vivo, in the liver and gonads. Treatment with estradiol, significantly upregulated transcript levels for all three types of ERs (ERalpha, ERbetaI, and ERbetaII) in the goldfish ovary and testis. In the goldfish liver, treatment with estradiol significantly increased ERalpha, ERbetaI transcript levels without affecting ERbetaII. In all cases increased ER transcript level was correlated with increased ER protein level determined by Western blot analysis, although we are not able to distinguish between ER subtypes. The results provide strong support for the hypothesis that homologous regulation of ERs is tissue- and gender-specific, and may be a mechanism for estrogen-mediated regulation of reproduction in goldfish.

Transient receptor potential channel 6-mediated, localized cytosolic [Na+] transients drive Na+/Ca2+ exchanger-mediated Ca2+ entry in purinergically stimulated aorta smooth muscle cells

The Na+/Ca2+ exchanger (NCX) is increasingly recognized as a physiological mediator of Ca2+ influx and significantly contributes to salt-sensitive hypertension. We recently reported that Ca2+ influx by the NCX (1) is the primary mechanism of Ca2+ entry in purinergically stimulated rat aorta smooth muscle cells and (2) requires functional coupling with transient receptor potential channel 6 nonselective cation channels. Using the Na+ indicator CoroNa Green, we now directly observed and characterized the localized cytosolic [Na+] ([Na+]i) elevations that have long been hypothesized to underlie physiological NCX reversal but that have never been directly shown. Stimulation of rat aorta smooth muscle cells caused both global and monotonic [Na+]i elevations and localized [Na+]i transients (LNats) at the cell periphery. Inhibition of nonselective cation channels with SKF-96365 (50 micromol/L) and 2-amino-4-phosphonobutyrate (75 micromol/L) reduced both global and localized [Na+]i elevations in response to ATP (1 mmol/L). This effect was mimicked by expression of a dominant negative construct of transient receptor potential channel 6. Selective inhibition of NCX-mediated Ca2+ entry with KB-R7943 (10 micromol/L) enhanced the LNats, whereas the global cytosolic [Na+] signal was unaffected. Inhibition of mitochondrial Na+ uptake with CGP-37157 (10 micromol/L) increased both LNats and global cytosolic [Na+] elevations. These findings directly demonstrate NCX regulation by LNats, which are restricted to subsarcolemmal, cytoplasmic microdomains. Analysis of the LNats, which facilitate Ca2+ entry via NCX, suggests that mitochondria limit the cytosolic diffusion of LNats generated by agonist-mediated activation of transient receptor potential channel 6-containing channels.