An Unexpected Lymphoma: A Rare Case of Primary Gastric Burkitt's Lymphoma.

Primary gastric Burkitt's lymphoma is an aggressive non-Hodgkin's lymphoma that has been rarely reported in the literature. The majority of primary gastric lymphomas are diffuse large B-cell lymphomas and mucosa-associated lymphoid tissue (MALT) lymphomas. Patients with primary gastric Burkitt's lymphoma can present with abdominal pain, hematemesis, melena, perforation, and obstruction. Diagnosis is made with a combination of clinical, radiological, and pathological findings. Treatment data are limited due to the limited cases reported. We present a case of a 47-year-old female who presented with diffuse abdominal pain, melena, and coffee-ground emesis that was diagnosed with primary gastric Burkitt's lymphoma following biopsies taken from a gastric ulcerated mass found on upper endoscopy.

A rare case of primary diffuse large B-cell lymphoma of the colon.

The gastrointestinal tract is the most common site in the United States for extra-nodal lymphoma involvement. Primary colorectal involvement is very rare, only accounting for 0.3% of the large intestine cancers. There has been a small increase in the incidence in these high-risk patient populations which include IBD, Celiac disease, H. pylori and other autoimmune diseases. We report a case of 47 years old male with no risk factors, who presented to the hospital with non-specific signs and symptoms. Imaging revealed cecal mass with distended bowel and colonoscopy revealed large mass obstructing the whole lumen of the cecum. The histopathology showed diffuse large B-cell lymphoma and patient underwent hemicolectomy. Chemotherapy was started and the patient improved.

Usefulness of PA32540 in Protecting the Gastric Layer While Providing Secondary Prevention for Coronary Artery Disease.

Aspirin has been the mainstay for secondary prevention of coronary artery disease to decrease early recurrence and severity of recurrent cardiovascular events. However, an increase in gastrointestinal bleeding due to aspirin is preventing many patients from adhering to this daily regimen. PA32540, a combination pill with aspirin and omeprazole, is a newly emerging intervention that has the potential to reinforce patient compliance with the aspirin regimen due to fewer gastrointestinal adverse effects. This systematic review assessed three recent phase 3 clinical trials investigating the safety and efficacy of PA32540. Clinical trials were chosen based on inclusion criteria such as phase 3, randomized, open-label or blinded studies, utilization of enteric-coated aspirin 325 mg dose, and measured GI adverse effects and major adverse cardiac events (MACE) as primary outcomes. Study A, a 6-month phase-3 study by Whellan et al., used two identically designed, randomized, double-blind trials to compare the GI adverse events and MACE after the use of PA32540 to 325mg of enteric coated Aspirin (EC-ASA) in subjects at risk for aspirin-associated gastric ulcers. Results showed fewer upper GI symptoms, decreased size of ulcers, and improved heartburn symptoms in subjects receiving PA32540 compared to EC-ASA. Study B, a 12-month phase-3 study by Hatoum et al., assessed secondary cardiovascular event prevention in a study population that was treated with PA32540 in comparison to a community setting (CS) group that was started on a standard antiplatelet treatment. Results indicated a 28% reduction of CV events in subjects treated with PA32540 compared to the CS group. Study C, a phase-3 open-label study by Goldstein et al., evaluating secondary prevention of cardiovascular/cerebrovascular events with the use of PA32450 for 12 months found that none of the 12-month completers were reported to have new-onset gastric ulcers. In conclusion, PA32540 could be an effective therapy for secondary prevention of coronary artery disease as studies are showing similar efficacy in preventing MACE with reduced GI side effects.

Erosive Esophagitis in the Obese: The Effect of Ethnicity and Gender on Its Association.

Background. Data examining the association between obesity and erosive esophagitis (ErE) have been inconsistent, with very little known about interracial variation. Goals. To examine the association between obesity and ErE among patients of different ethnic/racial backgrounds. Methods. The study sample included 2251 patients who underwent esophagogastroduodenoscopy (EGD). The effects of body mass index (BMI) on ErE were assessed by gender and in different ethnic groups. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using multivariate logistic regression analysis. Results. The prevalence of ErE was 29.4% (661/2251). Overweight and obese subjects were significantly more likely to have ErE than individuals with a normal BMI, with the highest risk seen in the morbidly obese (OR 6.26; 95% CI 3.82-10.28; p < 0.0001). Normal weight Black patients were less likely to have ErE as compared to Caucasians (OR 0.46; 95% CI 0.27-0.79; p = 0.005), while the odds ratio comparing normal weight Hispanics to normal weight Whites was not statistically significant. No effect modification was seen between BMI and race/ethnicity or BMI and gender. Significant trends were seen in each gender and ethnicity. Conclusions. The effect of BMI on ErE does not appear to vary by race/ethnicity or gender.

Hiatus Hernia: A Rare Cause of Acute Pancreatitis.

Hiatal hernia (HH) is the herniation of elements of the abdominal cavity through the esophageal hiatus of the diaphragm. A giant HH with pancreatic prolapse is very rare and its causing pancreatitis is an even more extraordinary condition. We describe a case of a 65-year-old man diagnosed with acute pancreatitis secondary to pancreatic herniation. In these cases, acute pancreatitis may be caused by the diaphragmatic crura impinging upon the pancreas and leading to repetitive trauma as it crosses the hernia; intermittent folding of the main pancreatic duct; ischemia associated with stretching at its vascular pedicle; or total pancreatic incarceration. Asymptomatic hernia may not require any treatment, while multiple studies have supported the recommendation of early elective repair as a safer route in symptomatic patients. In summary, though rare, pancreatic herniation should be considered as a cause of acute pancreatitis. A high index of suspicion for complications is warranted in cases like these.

Establishing the link between hepatitis B virus infection and colorectal adenoma.

BACKGROUND: Chronic hepatitis B (CHB) infection has been associated with malignancy, most notably hepatocellular carcinoma. Previous research has shown that hepatitis C is associated with increased colorectal adenomas and neoplasia. Currently, there are no studies on the association of CHB and colorectal adenomas. We aimed to identify a possible link between CHB and colorectal adenoma. METHODS: A retrospective chart review was performed on 588 consecutive patients undergoing screening or diagnostic colonoscopy that were previously screened or diagnosed with hepatitis B. Comparisons between categorical variables were analyzed with Chi Square test and t-test for continuous variables. Unconditional logistic regression was used to generate age-, gender-and race-adjusted odds ratios and their 95% confidence intervals (CI) comparing medication users with non-users. Statistical analyses were performed with SAS 9.3 software. RESULTS: A total of 487 patients were analyzed in the control group vs. 71 in the hepatitis B group. The adenoma detection rate was 23.9% in hepatitis B vs. 15.9% in the non-hepatitis B group for all cause colonoscopy; however this did not reach statistical significance. There was a significantly higher number of adenomas present in the distal colon compared to control (OR =2.16; 95% CI, 1.06-4.43; P=0.04). There were no significant findings between hepatitis B infection with size, multiplicity or presence of proximal adenomas. There was a significant difference noted in regards to smoking history, BMI and age between two groups. CONCLUSIONS: Although the adenoma detection rate was higher in hepatitis B population vs. the non-hepatitis B group this did not reach statistical significance. However, we did find an association between CHB infection and the presence of distal colorectal adenomas. Larger prospective studies are needed to strengthen our findings along with future studies examining hepatitis B virus (HBV) and mechanisms inducing colorectal carcinogenesis.

Low bone mineral density linked to colorectal adenomas: a cross-sectional study of a racially diverse population.

BACKGROUND: Epidemiologic studies suggest that lower bone mineral density (BMD) is associated with an increased risk for colorectal adenoma/cancer, especially in postmenopausal women. The aim of this study is to investigate the association between osteopenia and/or osteoporosis and colorectal adenomas in patients from a New York community hospital. METHODS: We performed a cross-sectional observational study on 200 patients who underwent screening colonoscopies and bone density scan (dual-energy X-ray absorptiometry) at Nassau University Medical Center from November 2009 to March 2011. Among these, 83 patients were identified as osteoporosis (T score of -2.5 or below) and 67 were osteopenia (T score between -1.0 and -2.5). Logistic regression model was performed to assess the association between osteopenia and/or osteoporosis and colorectal adenomas. RESULTS: Among the patients with osteopenia and osteoporosis, the mean ages were 59.1 years [standard deviation (SD) =8.9] and 61.5 (SD =8.9), respectively. There were 94.0%, 85.1% and 74.7% women, respectively, in normal BMD, osteopenia and osteoporosis groups. The prevalence of colorectal adenomas was 17.9% and 25.3% in the osteopenia and osteoporosis groups, respectively, and 18.0% in the normal BMD group. After adjustment for potential confounders including age, sex, race, body mass index (BMI), tobacco use, alcohol use, history of diabetes, hypertension, or dyslipidemia, osteoporosis was found to be associated with presence of colorectal adenomas more than 2, compared to the normal BMD group. No significant associations were found for the prevalence, size, and location of adenomas. CONCLUSIONS: Our study suggests that osteoporosis is significantly associated with the presence of multiple colorectal adenomas. Prospective studies with a larger sample size are warranted in the future.

Ethnic disparities in the risk of colorectal adenomas associated with lipid levels: a retrospective multiethnic study.

BACKGROUND: Although data exists showing that uncontrolled lipid levels in white and black patients is associated with colorectal adenomas, there are currently no studies looking only at the Hispanic population. PURPOSE: With the rapid increase in the Hispanic population, we aimed to look at their risk of colorectal adenomas in association with lipid levels. METHODS: We retrospectively analyzed 1473 patients undergoing colonoscopy from 2009 to 2011 at a community hospital. Statistical analysis was performed using Chi-squared for categorical variables and t test for continuous variables with age-, gender-, and race-adjusted odds ratios. Unconditional logistic regression model was used to estimate 95 % confidence intervals (CI). SAS 9.3 software was used to perform all statistical analysis. RESULTS: In our general population, there was an association with elevated triglyceride levels greater than 150 and presence of multiple colorectal adenomas with odds ratio (OR) 1.60 (1.03, 2.48). There was an association with proximal colon adenomas and cholesterol levels between 200 and 239 with OR 1.57 (1.07, 2.30), and low-density lipoprotein (LDL) levels of greater than 130 with OR 1.54 (1.04, 2.30). There was no association between high-density lipoproteins (HDL) levels and colorectal adenomas. The Hispanic population showed no statistical correlation between elevated triglycerides, cholesterol, or LDL with the presence, size, location, or multiplicity of colorectal adenomas. CONCLUSIONS: We found a significant correlation between elevated lipid levels and colorectal adenomas in white and black patients; however, there was no such association in the Hispanic population. This finding can possibly be due to environmental factors such as dietary, colonic flora, or genetic susceptibility, which fosters further investigation and research.

The association of H. pylori and colorectal adenoma: does it exist in the US Hispanic population?

BACKGROUND: Although data on the association between colorectal adenomas and Helicobacter pylori (H. pylori) exists in White and Black patients, there is no data on this association in a US Hispanic population. Our aim was to study the association of adenoma detection and biopsy proven H. pylori infection in a cohort of US Hispanics. METHODS: Data were collected from Nassau University Medical Center, a 530-bed tertiary care teaching hospital in East Meadow, New York. Patients who underwent both an esophagogastroduodenoscopy (EGD) and colonoscopy from July 2009 to March 2011 were pulled from an electronic database. A total of 1,737 patients completed colonoscopies during this time with 95 excluded: 17 inflammatory bowel disease, 12 malignancy, 22 prior history of colorectal adenoma, and 44 incomplete. Among the colonoscopies, 799 patients had EGD's performed prior to colonoscopies that were eligible for our study. RESULTS: H. pylori prevalence was highest in Hispanics 40.9%, followed by Blacks 29.1% (OR 0.59, 95% CI: 0.42-0.84), then Whites 7.9% (OR 0.12, 95% CI: 0.06-0.24). The adenoma detection rate was significantly higher in Whites 23.2% and Blacks 21.8% compared to Hispanics 14.5%, P=0.0002 respectively. Smoking and alcohol were lower in the H. pylori group, 18.6% (n=44) vs. 26.1% (n=147) for smoking (P=0.02) and 14.4% (n=34) vs. 19% (n=107) for alcohol (P=0.12), respectively. There was no evidence in the Hispanics for an association between adenoma detection and H. pylori infection. Furthermore size, location, and multiple polyps did not differ between the two groups. CONCLUSIONS: While data has shown an association between H. pylori and colorectal adenomas, we did not find this in our Hispanic population. With the growing population of Hispanics in the U.S, large scale studies are needed to conclusively characterize the role of H. pylori infection in colorectal adenoma and adenocarcinoma in this group of patients.

Ethnic disparities in the risk of colorectal adenomas associated with aspirin and statin use: a retrospective multiethnic study.

BACKGROUND: Although data on the inverse association between colorectal adenomas (CRA) and daily aspirin or statin therapy exists in white and black patients, scarce data exists on these associations in the Hispanic population. With a rapidly increasing Hispanic population in the United States, defining the association in Hispanics is crucial. METHODS: The study sample included 1,843 consecutive patients who underwent a colonoscopy (screening or diagnostic) from 2009 to 2011 at a community hospital in East Meadow, New York. Data was then extracted from patient charts regarding aspirin and/or statin use. Adjusted odds ratios (OR) and their 95% confidence intervals (CI) were calculated to assess the association between colonoscopy findings and aspirin, statin, or aspirin/statin use. RESULTS: In our total population including all races, aspirin user had an increased risk for having two or more adenomas (OR =1.73, 95% CI: 1.00, 2.99, P=0.05) and presence of an adenoma in the proximal colon (OR =1.66, 95% CI: 1.07, 2.58, P=0.02). In the total study population, those who used both statin and aspirin had an increased risk for having two or more adenomas (OR =2.56, 95% CI: 1.21, 5.39, P=0.01). In the Hispanic population, users of both medications had an increased risk for having two or more adenomas (OR =19.04, 95% CI: 1.30, 280.09, P=0.03), adenoma present in the distal colon (OR =5.75, 95% CI: 1.64, 20.21, P=0.01) and largest adenoma in distal colon (OR =5.75, 95% CI: 1.64, 20.21, P=0.01). CONCLUSIONS: Aspirin use and aspirin/statin use was associated with abnormal colonoscopy findings, particularly in the Hispanic population. These findings may be due to environmental factors such as dietary, colonic flora, or genetic susceptibility. The findings warrant further investigational research, particularly in Hispanics.

Rectal ulcers and massive bleeding after hemorrhoidal band ligation while on aspirin.

Endoscopic hemorrhoidal band ligation is a well-established nonoperative method for treatment of bleeding internal hemorrhoids (grade 1 to 3). It is a safe and effective technique with a high success rate. Complications with this procedure are uncommon. Although rectal ulceration due to band ligation is a rare complication, it can cause life-threatening hemorrhage especially when patients are on medications which impair hemostasis like aspirin or non steroidal anti-inflammatory drugs. We present 2 cases of massive lower gastro-intestinal bleeding in patients who had a band ligation procedure performed 2 wk prior to the presentation and were on aspirin at home. Both the patients were hemodynamically unstable requiring resuscitation. They required platelet and blood transfusions and were found to have rectal ulcers on colonoscopy done subsequently. The rectal ulcers corresponded to the site of band ligation. The use of aspirin by these patients would have caused defects in the hemostasis and may have predisposed them to massive bleeding in the presence of rectal ulcers occurring after the band ligation procedure. Managing aspirin before and after the ligation may be difficult especially since adequate guidelines are unavailable. Stopping aspirin in all the cases might not be safe and the decision should be individualized.

Functional Interactions between Distinct Sodium Channel Cytoplasmic Domains through the Action of Calmodulin.

Sodium channels are fundamental signaling molecules in excitable cells, and are molecular targets for local anesthetic agents and intracellular free Ca(2+) ([Ca(2+)](i)). Two regions of Na(V)1.5 have been identified previously as [Ca(2+)](i)-sensitive modulators of channel inactivation. These include a C-terminal IQ motif that binds calmodulin (CaM) in different modes depending on Ca(2+) levels, and an immediately adjacent C-terminal EF-hand domain that directly binds Ca(2+). Here we show that a mutation of the IQ domain (A1924T; Brugada Syndrome) that reduces CaM binding stabilizes Na(V)1.5 inactivation, similarly and more extensively than even reducing [Ca(2+)](i). Because the DIII-DIV linker is an essential structure in Na(V)1.5 inactivation, we evaluated this domain for a potential CaM binding interaction. We identified a novel CaM binding site within the linker, validated its interaction with CaM by NMR spectroscopy, and revealed its micromolar affinity by isothermal titration calorimetry. Mutation of three consecutive hydrophobic residues (Phe(1520)-Ile(1521)-Phe(1522)) to alanines in this CaM-binding domain recapitulated the electrophysiology phenotype observed with mutation of the C-terminal IQ domain: Na(V)1.5 inactivation was stabilized; moreover, mutations of either CaM-binding domain abolish the well described stabilization of inactivation by lidocaine. The direct physical interaction of CaM with the C-terminal IQ domain and the DIII-DIV linker, combined with the similarity in phenotypes when CaM-binding sites in either domain are mutated, suggests these cytoplasmic structures could be functionally coupled through the action of CaM. These findings have bearing upon Na(+) channel function in genetically altered channels and under pathophysiologic conditions where [Ca(2+)](i) impacts cardiac conduction.

Sex, age, and regional differences in L-type calcium current are important determinants of arrhythmia phenotype in rabbit hearts with drug-induced long QT type 2.

In congenital and acquired long QT type 2, women are more vulnerable than men to torsade de pointes. In prepubertal rabbits (and children), the arrhythmia phenotype is reversed; however, females still have longer action potential durations than males. Thus, sex differences in K(+) channels and action potential durations alone cannot account for sex-dependent arrhythmia phenotypes. The L-type calcium current (I(Ca,L)) is another determinant of action potential duration, Ca(2+) overload, early afterdepolarizations (EADs), and torsade de pointes. Therefore, sex, age, and regional differences in I(Ca,L) density and in EAD susceptibility were analyzed in epicardial left ventricular myocytes isolated from the apex and base of prepubertal and adult rabbit hearts. In prepubertal rabbits, peak I(Ca,L) at the base was 22% higher in males than females (6.4+/-0.5 versus 5.0+/-0.2 pA/pF; P<0.03) and higher than at the apex (6.4+/-0.5 versus 5.0+/-0.3 pA/pF; P<0.02). Sex differences were reversed in adults: I(Ca,L) at the base was 32% higher in females than males (9.5+/-0.7 versus 6.4+/-0.6 pA/pF; P<0.002) and 28% higher than the apex (9.5+/-0.7 versus 6.9+/-0.5 pA/pF; P<0.01). Apex-base differences in I(Ca,L) were not significant in adult male and prepubertal female hearts. Western blot analysis showed that Ca(v)1.2alpha levels varied with sex, maturity, and apex-base, with differences similar to variations in I(Ca,L); optical mapping revealed that the earliest EADs fired at the base. Single myocyte experiments and Luo-Rudy simulations concur that I(Ca,L) elevation promotes EADs and is an important determinant of long QT type 2 arrhythmia phenotype, most likely by reducing repolarization reserve and by enhancing Ca(2+) overload and the propensity for I(Ca,L) reactivation.

Potential role of isoketals formed via the isoprostane pathway of lipid peroxidation in ischemic arrhythmias.

Unabated reactive oxygen species (ROS) are potentiated by an ischemia-induced shift in anaerobic metabolism, which generates superoxide anion upon reperfusion and reintroduction of oxygen. ROS can modify protein structure and function in fundamental ways, one of which is by forming reactive lipid species from the oxidation of lipids. In this review, we discuss these pathways and discuss the literature that shows that these species can produce dramatic effects on cardiac ion channel function (eg, Na+ channel function). Furthermore, we review what is known about the generation of such in the highly remodeled post myocardial infarction substrate. We suggest prevention of adduction of these highly reactive compounds would be antiarrhythmic.

Mutation in glycerol-3-phosphate dehydrogenase 1 like gene (GPD1-L) decreases cardiac Na+ current and causes inherited arrhythmias.

BACKGROUND: Brugada syndrome is a rare, autosomal-dominant, male-predominant form of idiopathic ventricular fibrillation characterized by a right bundle-branch block and ST elevation in the right precordial leads of the surface ECG. Mutations in the cardiac Na+ channel SCN5A on chromosome 3p21 cause approximately 20% of the cases of Brugada syndrome; most mutations decrease inward Na+ current, some by preventing trafficking of the channels to the surface membrane. We previously used positional cloning to identify a new locus on chromosome 3p24 in a large family with Brugada syndrome and excluded SCN5A as a candidate gene. METHODS AND RESULTS: We used direct sequencing to identify a mutation (A280V) in a conserved amino acid of the glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) gene. The mutation was present in all affected individuals and absent in >500 control subjects. GPD1-L RNA and protein are abundant in the heart. Compared with wild-type GPD1-L, coexpression of A280V GPD1-L with SCN5A in HEK cells reduced inward Na+ currents by approximately 50% (P<0.005). Wild-type GPD1-L localized near the cell surface to a greater extent than A280V GPD1-L. Coexpression of A280V GPD1-L with SCN5A reduced SCN5A cell surface expression by 31+/-5% (P=0.01). CONCLUSIONS: GPD1-L is a novel gene that may affect trafficking of the cardiac Na+ channel to the cell surface. A GPD1-L mutation decreases SCN5A surface membrane expression, reduces inward Na+ current, and causes Brugada syndrome.

A sodium channel pore mutation causing Brugada syndrome.

BACKGROUND: Brugada and long QT type 3 syndromes are linked to sodium channel mutations and clinically cause arrhythmias that lead to sudden death. We have identified a novel threonine-to-isoleucine missense mutation at position 353 (T353I) adjacent to the pore-lining region of domain I of the cardiac sodium channel (SCN5A) in a family with Brugada syndrome. Both male and female carriers are symptomatic at young ages, have typical Brugada-type electrocardiogram changes, and have relatively normal corrected QT intervals. OBJECTIVES: To characterize the properties of the newly identified cardiac sodium channel (SCN5A) mutation at the cellular level. RESULTS: Using whole-cell voltage clamp, we found that heterologous expression of SCN5A containing the T353I mutation resulted in 74% +/- 6% less peak macroscopic sodium current when compared with wild-type channels. A construct of the T353I mutant channel fused with green fluorescent protein failed to traffic properly to the sarcolemma, with a large proportion of channels sequestered intracellularly. Overnight exposure to 0.1 mM mexiletine, a Na(+) channel blocking agent, increased T353I channel trafficking to the membrane to near normal levels, but the mutant channels showed a significant late current that was 1.6% +/- 0.2% of peak sodium current at 200 ms, a finding seen with long QT mutations. CONCLUSIONS: The clinical presentation of patients carrying the T353I mutation is that of Brugada syndrome and could be explained by a cardiac Na(+) channel trafficking defect. However, when the defect was ameliorated, the mutated channels had biophysical properties consistent with long QT syndrome. The lack of phenotypic changes associated with the long QT syndrome could be explained by a T353I-induced trafficking defect reducing the number of mutant channels with persistent currents present at the sarcolemma.

HERG is protected from pharmacological block by alpha-1,2-glucosyltransferase function.

The HERG (human ether-à-go-go-related gene) protein, which underlies the cardiac repolarizing current I(Kr), is the unintended target for many pharmaceutical agents. Inadvertent block of I(Kr), known as the acquired long QT syndrome (aLQTS), is a leading cause for drug withdrawal by the United States Food and Drug Administration. Hence, an improved understanding of the regulatory factors that protect most individuals from aLQTS is essential for advancing clinical therapeutics in broad areas, from cancer chemotherapy to antipsychotics and antidepressants. Here, we show that the K(+) channel regulatory protein KCR1, which markedly reduces I(Kr) drug sensitivity, protects HERG through glucosyltransferase function. KCR1 and the yeast alpha-1,2-glucosyltransferase ALG10 exhibit sequence homology, and like KCR1, ALG10 diminished HERG block by dofetilide. Inhibition of cellular glycosylation pathways with tunicamycin abrogated the effects of KCR1, as did expression in Lec1 cells (deficient in glycosylation). Moreover, KCR1 complemented the growth defect of an alg10-deficient yeast strain and enhanced glycosylation of an Alg10 substrate in yeast. HERG itself is not the target for KCR1-mediated glycosylation because the dofetilide response of glycosylation-deficient HERG(N598Q) was still modulated by KCR1. Nonetheless, our data indicate that the alpha-1,2-glucosyltransferase function is a key component of the molecular pathway whereby KCR1 diminishes I(Kr) drug response. Incorporation of in vitro data into a computational model indicated that KCR1 expression is protective against arrhythmias. These findings reveal a potential new avenue for targeted prevention of aLQTS.

Quantitation of protein kinase A-mediated trafficking of cardiac sodium channels in living cells.

OBJECTIVE: Na(+) current derived from expression of the principal cardiac Na(+) channel, Na(v)1.5, is increased by activation of protein kinase A (PKA). This effect is blocked by inhibitors of cell membrane recycling, or removal of a cytoplasmic endoplasmic reticulum (ER) retention motif, suggesting that PKA stimulation increases trafficking of cardiac Na(+) channels to the plasma membrane. METHODS: To test this hypothesis, green fluorescent protein (GFP) was fused to Na(v)1.5 (Na(v)1.5-GFP), and the effects of PKA activation were investigated in intact, living cells that stably expressed the fusion protein. Using confocal microscopy, the spatial relationship of GFP-tagged channels relative to the plasma membrane was quantitated using a measurement that could control for variables present during live-cell imaging, and permit an unbiased analysis for all cells in a given field. RESULTS: In the absence of kinase stimulation, intracellular fluorescence representing Na(v)1.5-GFP channels was greatest in the perinuclear area, with additional concentration of channels beneath the cell surface. Activation of PKA promoted trafficking of Na(+) channels from both regions to the plasma membrane. Experimental results using a chemiluminescence-based assay further confirmed that PKA stimulation increased expression of Na(v)1.5 channels at the cell membrane. CONCLUSIONS: Our results provide direct evidence for PKA-mediated trafficking of cardiac Na(+) channels into the plasma membrane in living, mammalian cells, and they support the existence of multiple intracellular storage pools of channel protein that can be mobilized following a physiologic stimulus.

Recreating an artificial biological pacemaker: insights from a theoretical model.

BACKGROUND: Normal cardiac rhythm is critically dependent on the sinoatrial (SA) node, the natural biological pacemaker. Although recent studies have focused on the development of "artificial" biological pacemakers using gene transfer, less is known about the functional consequences of such interventions. OBJECTIVE: The purpose of this study was to investigate the electrophysiological consequences of two approaches used to create a biological pacemaker: overexpression of the hyperpolarization-activated cyclic nucleotide gated channel (HCN "pacemaker" channels) and suppression of the inward-rectifier potassium current, I(K1). METHODS: We used a linear multicellular Luo-Rudy (LRd) AP model consisting of 130 ventricular cells connected by resistive gap junctions. To induce automaticity, I(K1) current was reduced or I(f) (HCN) current was introduced in endocardial and midmyocardial (M) cells. RESULTS: Similar to the previously published results for a single LRd model, myocyte I(K1) suppression induced automaticity in the fiber. While introduction of I(f) also resulted in automaticity, the main differences between I(K1) suppression and I(f) expression were (1) a relatively more gradual phase 4 depolarization with HCN expression, (2) stabilization of cycle lengths during I(K1) suppression, but not during HCN expression, and (3) responsiveness to beta-adrenergic stimulation during HCN expression, but not during I(K1) suppression. Upon further investigation, we found that cycle length instability during HCN expression was primarily due to a gradual reduction of intracellular potassium ([K(+)](i)) from its baseline value of 142 mM to 120 mM in 600 beats and subsequent alteration of potassium-dependent ionic currents. A twofold increase in HCN expression also led to a similar behavior. We attribute this decrease in [K(+)](i) to a large I(K1) during phase 4 depolarization. When intracellular [K(+)](i) loss was minimized, cycle lengths stabilized during HCN expression. CONCLUSIONS: Our results help to further understand the electrophysiologic consequences as well as some of the challenges associated with the creation of biological pacemakers using HCN and I(K1) gene transfer strategies.