Bioelectricity

Plants and bacteria are often used in combination with pulsed electric fields (PEFs) to improve processes or quality parameters. Although microbial inactivation is a common goal from the usage of this technology, the induction of a stress response, stimulation, or increased mass transfer can enhance subsequent cellular operations. These effects can be observed after sublethal PEF exposures, which require much lower energy inputs compared with lethal exposures. This work reviews the current state of literature regarding the beneficial effects of sublethal PEF exposures on plants and bacteria, and how they can be used to improve current processes.

Although membrane potentials (V_ms) are fundamental to the functioning broadly of all cell types, V_m dynamics have mostly been studied in the so-called “excitable” cells (mainly neurons and muscles). The various microelectrode techniques used to study V_ms, however, can suffer from significant limitations. For example, accessing the cell interior with the recoding pipette can produce adverse effects by dialyzing the cytoplasm, and the point nature of measurements makes it difficult to decipher any local or distributed change in V_m. Furthermore, the recoding is limited to one or just a few cells and there is need for high-level mechanical stability to maintain the recording electrode in/on the cell. This review has two attributes. First, we cover optical probes as voltage-sensitive indicators (VSIs) for imaging V_ms. Second, we illustrate the range of applications of VSIs to understand the bioelectricity of classically “nonexcitable” cells. Such VSIs comprise voltage-sensitive dyes (VSDs) and genetically encoded voltage indicators. Applications include common epithelial cells and tissues, blood cells (including lymphocytes and macrophages), and prokaryotic cells (bacteria). Both physiological and pathophysiological conditions are considered. In particular, a recent study involving the application of a fast VSD to human metastatic breast cancer cells revealed that V_m is not static, but undergoes spontaneous hyperpolarizing voltage transients (HVTs) in a subpopulation of cells. These HVTs were inhibited by tetrodotoxin, consistent with the cells having basal voltage-gated sodium channel activity. In contrast, normal breast epithelial cells demonstrated very few HVTs, but these could be induced by treating the cells with transforming growth factor-β. The latter is known to promote epithelial-to-mesenchymal transition, an early event in cancer invasiveness. Taken together, these observations suggest that HVTs could play a functional role in the cancer process. We conclude that VSIs have much potential in improving our understanding of cellular bioelectricity, physiology, and pathophysiology.

Clusters of the α-subunit of voltage-gated sodium (Na_v) channels have been observed in various tissues and are recognized as key regulators of cellular excitability and action potential propagation. In cardiomyocytes, the most abundant Na_v α-subunit, Na_v1.5, is expressed at specialized membrane microdomains within the intercalated disk and lateral membrane. Although Na_v1.5 remodeling within these microdomains could cause abnormal cardiac phenotypes, the molecular mechanisms underlying single-molecule redistribution and biophysical cooperativity of Na_v1.5 remain not fully understood. This review summarizes the current knowledge on the oligomerization of Na_v1.5. In particular, direct α–α-subunit interactions and oligomerization through intermediary proteins such as Na_vβ-subunits and 14–3–3 proteins are discussed. The possible implication of Na_v1.5 oligomerization in the coupled gating in cis and trans conformations as well as in the dominant-negative effect is reviewed.

Blood vessels are highly organized and form during development through a series of complex processes that include vasculogenesis, sprouting angiogenesis, and vessel remodeling. Several gap junction proteins (termed connexins, Cx)—including Cx40 (GJA5)—are expressed in vascular endothelium early during vessel development and are critical for establishment of a healthy vasculature. However, Cx40's specific role in regulating vessel growth remains uncertain: while previous studies have shown that developmental and cancer-associated neovascularization is reduced in Cx40-knockout mice, Cx40 knockout in zebrafish embryos enhances intersegmental vessel growth. Thus, in the current study, our aim was to identify Cx40's specific role in sprouting angiogenesis. First, we used a vessel-on-a-chip microphysiological model to confirm Cx40's overall necessity for microvessel network development. Next, we used the fibrin gel bead assay—a three-dimensional in vitro model of sprouting angiogenesis—to assess Cx40's necessity for this process. We found that Cx40 knockdown in endothelial cells (EC) drives more aggressive sprouting angiogenesis in association with increased EC proliferation. By contrast, using electrical cell-substrate impedance sensing we observed no effect of Cx40 knockdown on EC migration. Finally, we found that Cx37 (GJA4) is reduced in Cx40-deficient EC and that targeted silencing of Cx37 alone produces a more aggressive, hypersprouting phenotype compared to control or Cx40 knockdown EC. Taken together, our data indicate that Cx40 plays multiple roles during vessel growth, including to specifically limit sprouting angiogenesis, and that this may occur, at least in part, through regulation of endothelial Cx37 levels.