Kevin Prestia

Increased Cell-Cell Coupling Increases Infarct Size and Does not Decrease Incidence of Ventricular Tachycardia in Mice.

Increasing connexin43 (Cx43) gap junctional conductance as a means to improve cardiac conduction has been proposed as a novel antiarrhythmic modality. Yet, transmission of molecules via gap junctions may be associated with increased infarct size. To determine whether maintaining open gap junction channels impacts on infarct size and induction of ventricular tachycardia (VT) following coronary occlusion, we expressed the pH- and voltage-independent connexin isoform connexin32 (Cx32) in ventricle and confirmed Cx32 expression. Wild-type (WT) mice injected with adenovirus-Cx32 (Cx32inj) were examined following coronary occlusion to determine infarct size and inducibility of VT. There was an increased infarct size in Cx32inj hearts as compared to WT (WT 22.9u2009±u20094%; Cx32inj 44.3u2009±u20095%; pu2009<u20090.05). Programmed electrical stimulation showed no difference in VT inducibility in WT and Cx32inj mice (VT was reproducibly inducible in 55% of shams and 50% of Cx32inj mice (pu2009>u20090.05). Following coronary occlusion, improving cell–cell communication increased infarct size, and conferred no antiarrhythmic benefit.

Transfusion of stored blood impairs host defenses against Gram-negative pathogens in mice.

Although human red blood cell (RBC) units may be refrigerator stored for up to 42 days, transfusion of older RBCs acutely delivers a large bolus of iron to mononuclear phagocytes. Similarly, iron dextran circulates in plasma for hours to days and is progressively cleared by mononuclear phagocytes, which return iron to plasma. Finally, malaria infection continuously delivers iron to macrophages by intra‐ and extravascular hemolysis. Studies suggest that iron administration increases infectious risk.

Expression of Skeletal Muscle Sodium Channel (Nav1.4) or Connexin32 Prevents Reperfusion Arrhythmias in Murine Heart

AIMSnacute myocardial ischaemia induces a decrease in resting membrane potential [which leads to reduction of action potential (AP) V(max)] and intracellular acidification (which closes gap junctions). Both contribute to conduction slowing. We hypothesized that ventricular expression of the skeletal muscle Na(+) channel, Nav1.4 (which activates fully at low membrane potentials), or connexin32 (Cx32, which is less pH-sensitive than connexin43) would support conduction and be antiarrhythmic. We tested this hypothesis in a murine model of ischaemia and reperfusion arrhythmias.nnnMETHODS AND RESULTSnempty adenovirus (Sham) or adenoviral constructs expressing either SkM1 (gene encoding Nav1.4) or Cx32 genes were injected into the left ventricular wall. Four days later, ventricular tachycardia (VT) occurred during reperfusion following a 5 min coronary occlusion. In Nav1.4- and Cx32-expressing mice, VT incidence and duration were lower than in Sham (P < 0.05). In vitro multisite microelectrode mapping was performed in the superfused right ventricular wall. To simulate ischaemic conditions, [K(+)] in solution was increased to 10 mmol/L and/or pH was decreased to 6.0. Western blots revealed Cx32 and Nav1.4 expression in both ventricles. Nav1.4 APs showed higher V(max) and conduction velocity (CV) than Shams at normal and elevated [K(+)]. Exposure of tissue to acid solution reduced intracellular pH to 6.4. There was no difference in CV between Sham and Cx32 groups in control solution. Acid solution slowed CV in Sham (P < 0.05) but not in Cx32.nnnCONCLUSIONnNav1.4 or Cx32 expression preserved normal conduction in murine hearts and decreased the incidence of reperfusion VT.

Cardiac expression of skeletal muscle sodium channels increases longitudinal conduction velocity in the canine 1-week myocardial infarction

BACKGROUNDnSkeletal muscle sodium channel (Nav1.4) expression in border zone myocardium increases action potential upstroke velocity in depolarized isolated tissue. Because resting membrane potential in the 1-week canine infarct is reduced, we hypothesized that conduction velocity (CV) is greater in Nav1.4 dogs compared with in control dogs.nnnOBJECTIVEnThe purpose of this study was to measure CV in the infarct border zone border in dogs with and without Nav1.4 expression.nnnMETHODSnAdenovirus was injected in the infarct border zone in 34 dogs. The adenovirus incorporated the Nav1.4- and a green fluorescent protein (GFP) gene (Nav1.4 group, n = 16) or only GFP (n = 18). After 1 week, upstroke velocity and CV were measured by sequential microelectrode recordings at 4 and 7 mM [K(+)] in superfused epicardial slabs. High-density in vivo epicardial activation mapping was performed in a subgroup (8 Nav1.4, 6 GFP) at three to four locations in the border zone. Microscopy and antibody staining confirmed GFP or Nav1.4 expression.nnnRESULTSnInfarct sizes were similar between groups (30.6% +/- 3% of left ventricle mass, mean +/- standard error of the mean). Longitudinal CV was greater in Nav1.4 than in GFP sites (58.5 +/- 1.8 vs. 53.3 +/- 1.2 cm/s, 20 and 15 sites, respectively; P <.05). Transverse CV was not different between the groups. In tissue slabs, dV/dt(max) was higher and CV was greater in Nav1.4 than in control at 7 mM [K(+)] (P <.05). Immunohistochemical Nav1.4 staining was seen at the longitudinal ends of the myocytes.nnnCONCLUSIONnNav1.4 channels in myocardium surviving 1 week infarction increases longitudinal but not transverse CV, consistent with the increased dV/dt(max) and with the cellular localization of Nav1.4.

Revisiting approval protocols: re-review not required.

Care and Use of Laboratory Animals3 require the IACUC to carry out continuing review of a protocol no less than annually1. Under certain circumstances, such as in situations of protocol non-compliance, the IACUC is also obliged to conduct an investigation. If warranted, the IACUC may convene to re-review the protocol and take appropriate action1. In this case, however, there is no such basis for Wilson’s request for re-review of the protocol. Furthermore, granting his request would supplant the authority of the IACUC and DMR process. At the time of annual renewal, Wilson would be free to review Ross’ progress report and express any reservations at that time. In conclusion, we believe that Covelli acted within the word and spirit of existing federal regulations.