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Browsing Department of Biological Sciences by Department "Biomedical Engineering and Mechanics"
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- The adhesion function of the sodium channel beta subunit (beta 1) contributes to cardiac action potential propagationVeeraraghavan, Rengasayee; Hoeker, Gregory S.; Alvarez-Laviada, Anita; Hoagland, Daniel T.; Wan, Xiaoping; King, D. Ryan; Sanchez-Alonso, Jose; Chen, Chunling; Jourdan, L. Jane; Isom, Lori L.; Deschenes, Isabelle; Smith, James W.; Gorelik, Julia; Poelzing, Steven; Gourdie, Robert G. (2018-08-14)Computational modeling indicates that cardiac conduction may involve ephaptic coupling - intercellular communication involving electrochemical signaling across narrow extracellular clefts between cardiomyocytes. We hypothesized that beta 1(SCN1B) - mediated adhesion scaffolds trans-activating Na(V)1.5 (SCN5A) channels within narrow (<30 nm) perinexal clefts adjacent to gap junctions (GJs), facilitating ephaptic coupling. Super-resolution imaging indicated preferential beta 1 localization at the perinexus, where it co-locates with Na(V)1.5. Smart patch clamp (SPC) indicated greater sodium current density (I-Na) at perinexi, relative to non-junctional sites. A novel, rationally designed peptide, beta adp1, potently and selectively inhibited beta 1-mediated adhesion, in electric cell-substrate impedance sensing studies. beta adp1 significantly widened perinexi in guinea pig ventricles, and selectively reduced perinexal I-Na, but not whole cell I-Na, in myocyte monolayers. In optical mapping studies, beta adp1 precipitated arrhythmogenic conduction slowing. In summary, beta 1-mediated adhesion at the perinexus facilitates action potential propagation between cardiomyocytes, and may represent a novel target for anti-arrhythmic therapies.
- Elevated perfusate [Na+] increases contractile dysfunction during ischemia and reperfusionKing, D. Ryan; Padget, Rachel L.; Perry, Justin B.; Hoeker, Gregory S.; Smyth, James W.; Brown, David A.; Poelzing, Steven (2020-10-14)Recent studies revealed that relatively small changes in perfusate sodium ([Na+](o)) composition significantly affect cardiac electrical conduction and stability in contraction arrested ex vivo Langendorff heart preparations before and during simulated ischemia. Additionally, [Na+](o) modulates cardiomyocyte contractility via a sodium-calcium exchanger (NCX) mediated pathway. It remains unknown, however, whether modest changes to [Na+](o) that promote electrophysiologic stability similarly improve mechanical function during baseline and ischemia-reperfusion conditions. The purpose of this study was to quantify cardiac mechanical function during ischemia-reperfusion with perfusates containing 145 or 155 mM Na+ in Langendorff perfused isolated rat heart preparations. Relative to 145 mM Na+, perfusion with 155 mM [Na+](o) decreased the amplitude of left-ventricular developed pressure (LVDP) at baseline and accelerated the onset of ischemic contracture. Inhibiting NCX with SEA0400 abolished LVDP depression caused by increasing [Na+](o) at baseline and reduced the time to peak ischemic contracture. Ischemia-reperfusion decreased LVDP in all hearts with return of intrinsic activity, and reperfusion with 155 mM [Na+](o) further depressed mechanical function. In summary, elevating [Na+](o) by as little as 10 mM can significantly modulate mechanical function under baseline conditions, as well as during ischemia and reperfusion. Importantly, clinical use of Normal Saline, which contains 155 mM [Na+](o), with cardiac ischemia may require further investigation.
- Heart Rate and Extracellular Sodium and Potassium Modulation of Gap Junction Mediated Conduction in Guinea PigsEntz, Michael, II; George, Sharon A.; Zeitz, Michael J.; Raisch, Tristan B.; Smyth, James W.; Poelzing, Steven (Frontiers, 2016-02-02)Background: Recent studies suggested that cardiac conduction in murine hearts with narrow perinexi and 50% reduced connexin43 (Cx43) expression is more sensitive to relatively physiological changes of extracellular potassium ([K+](o)) and sodium ([Na+](o)). Purpose: Determine whether similar [K+](o) and [Na+](o) changes alter conduction velocity (CV) sensitivity to pharmacologic gap junction (GJ) uncoupling in guinea pigs. Methods: [K+](o) and [Na+](o) were varied in Langendorff perfused guinea pig ventricles (Solution A: [K+](o) = 4.56 and [N+](o) = 153.3 mM. Solution B: [K+](o) = 6.95 and [Na+](o) = 145.5 mM). Gap junctions were inhibited with carbenoxolone (CBX) (15 and 30 mu M). Epicardial CV was quantified by optical mapping. Perinexal width was measured with transmission electron microscopy. Total and phosphorylated Cx43 were evaluated by western blotting. Results: Solution composition did not alter CV under control conditions or with 15 mu M CBX. Decreasing the basic cycle length (BCL) of pacing from 300 to 160 ms decreased CV uniformly with both solutions. At 30 mu M CBX, a change in solution did not alter CV either longitudinally or transversely at BCL = 300 ms. However, reducing BCL to 160 ms caused CV to decrease more in hearts perfused with Solution B than A. Solution composition did not alter perinexal width, nor did it change total or phosphorylated serine 368 Cx43 expression. These data suggest that the solution dependent CV changes were independent of altered perinexal width or GJ coupling. Action potential duration was always shorter in hearts perfused with Solution B than A. independent of pacing rate and/or CBX concentration. Conclusions: Increased heart rate and GJ uncoupling can unmask small CV differences caused by changing [K+](o) and [Na+](o). These data suggest that modulating extracellular ionic composition may be a novel anti-arrhythmic target in diseases with abnormal GJ coupling, particularly when heart rate cannot be controlled.
- Immunomagnetic separation of tumor initiating cells by screening two surface markersSun, Chen; Hsieh, Yuan-Pang; Ma, Sai; Geng, Shuo; Cao, Zhenning; Li, Liwu; Lu, Chang (Springer Nature, 2017-01-11)Isolating tumor initiating cells (TICs) often requires screening of multiple surface markers, sometimes with opposite preferences. This creates a challenge for using bead-based immunomagnetic separation (IMS) that typically enriches cells based on one abundant marker. Here, we propose a new strategy that allows isolation of CD44(+)/CD24(-) TICs by IMS involving both magnetic beads coated by anti-CD44 antibody and nonmagnetic beads coated by anti-CD24 antibody (referred to as two-bead IMS). Cells enriched with our approach showed significant enhancement in TIC marker expression (examined by flow cytometry) and improved tumorsphere formation efficiency. Our method will extend the application of IMS to cell subsets characterized by multiple markers.
- Modeling iontophoretic drug delivery in a microfluidic deviceMoarefian, Maryam; Davalos, Rafael V.; Tafti, Danesh K.; Achenie, Luke E. K.; Jones, Caroline N. (2020-09-21)Iontophoresis employs low-intensity electrical voltage and continuous constant current to direct a charged drug into a tissue. Iontophoretic drug delivery has recently been used as a novel method for cancer treatment in vivo. There is an urgent need to precisely model the low-intensity electric fields in cell culture systems to optimize iontophoretic drug delivery to tumors. Here, we present an iontophoresis-on-chip (IOC) platform to precisely quantify carboplatin drug delivery and its corresponding anti-cancer efficacy under various voltages and currents. In this study, we use an in vitro heparin-based hydrogel microfluidic device to model the movement of a charged drug across an extracellular matrix (ECM) and in MDA-MB231 triple-negative breast cancer (TNBC) cells. Transport of the drug through the hydrogel was modeled based on diffusion and electrophoresis of charged drug molecules in the direction of an oppositely charged electrode. The drug concentration in the tumor extracellular matrix was computed using finite element modeling of transient drug transport in the heparin-based hydrogel. The model predictions were then validated using the IOC platform by comparing the predicted concentration of a fluorescent cationic dye (Alexa Fluor 594 (R)) to the actual concentration in the microfluidic device. Alexa Fluor 594 (R) was used because it has a molecular weight close to paclitaxel, the gold standard drug for treating TNBC, and carboplatin. Our results demonstrated that a 50 mV DC electric field and a 3 mA electrical current significantly increased drug delivery and tumor cell death by 48.12% +/- 14.33 and 39.13% +/- 12.86, respectively (n = 3, p-value <0.05). The IOC platform and mathematical drug delivery model of iontophoresis are promising tools for precise delivery of chemotherapeutic drugs into solid tumors. Further improvements to the IOC platform can be made by adding a layer of epidermal cells to model the skin.
- Wind-driven spume droplet production and the transport of Pseudomonas syringae from aquatic environmentsPietsch, Renee B.; Grothe, Hinrich; Hanlon, Regina; Powers, Craig W.; Jung, Sunghwan; Ross, Shane D.; Schmale, David G. III (PeerJ, 2018-09-26)Natural aquatic environments such as oceans, lakes, and rivers are home to a tremendous diversity of microorganisms. Some may cross the air-water interface within droplets and become airborne, with the potential to impact the Earth’s radiation budget, precipitation processes, and spread of disease. Larger droplets are likely to return to the water or adjacent land, but smaller droplets may be suspended in the atmosphere for transport over long distances. Here, we report on a series of controlled laboratory experiments to quantify wind-driven droplet production from a freshwater source for low wind speeds. The rate of droplet production increased quadratically with wind speed above a critical value (10-m equivalent 5.7 m/s) where droplet production initiated. Droplet diameter and ejection speeds were fit by a gamma distribution. The droplet mass flux and momentum flux increased with wind speed. Two mechanisms of droplet production, bubble bursting and fragmentation, yielded different distributions for diameter, speed, and angle. At a wind speed of about 3.5 m/s, aqueous suspensions of the ice-nucleating bacterium Pseudomonas syringae were collected at rates of 283 cells m−2 s−1 at 5 cm above the water surface, and at 14 cells m−2 s−1 at 10 cm above the water surface. At a wind speed of about 4.0 m/s, aqueous suspensions of P. syringae were collected at rates of 509 cells m−2 s−1 at 5 cm above the water surface, and at 81 cells m−2 s−1 at 10 cm above the water surface. The potential for microbial flux into the atmosphere from aquatic environments was calculated using known concentrations of bacteria in natural freshwater systems. Up to 3.1 × 104 cells m−2 s−1 of water surface were estimated to leave the water in potentially suspended droplets (diameters <100 µm). Understanding the sources and mechanisms for bacteria to aerosolize from freshwater aquatic sources may aid in designing management strategies for pathogenic bacteria, and could shed light on how bacteria are involved in mesoscale atmospheric processes.