Approaches to Study Gap Junctional Coupling

Astrocytes and oligodendrocytes are main players in the brain to ensure ion and neurotransmitter homeostasis, metabolic supply, and fast action potential propagation in axons. These functions are fostered by the formation of large syncytia in which mainly astrocytes and oligodendrocytes are directly coupled. Panglial networks constitute on connexin-based gap junctions in the membranes of neighboring cells that allow the passage of ions, metabolites, and currents. However, these networks are not uniform but exhibit a brain region-dependent heterogeneous connectivity influencing electrical communication and intercellular ion spread. Here, we describe different approaches to analyze gap junctional communication in acute tissue slices that can be implemented easily in most electrophysiology and imaging laboratories. These approaches include paired recordings, determination of syncytial isopotentiality, tracer coupling followed by analysis of network topography, and wide field imaging of ion sensitive dyes. These approaches are capable to reveal cellular heterogeneity causing electrical isolation of functional circuits, reduced ion-transfer between different cell types, and anisotropy of tracer coupling. With a selective or combinatory use of these methods, the results will shed light on cellular properties of glial cells and their contribution to neuronal function.

Connexin Mutants Compromise the Lens Circulation and Cause Cataracts through Biomineralization

Gap junction-mediated intercellular communication facilitates the circulation of ions, small molecules, and metabolites in the avascular eye lens. Mutants of the lens fiber cell gap junction proteins, connexin46 (Cx46) and connexin50 (Cx50), cause cataracts in people and in mice. Studies in mouse models have begun to elucidate the mechanisms by which these mutants lead to cataracts. The expression of the dominant mutants causes severe decreases in connexin levels, reducing the gap junctional communication between lens fiber cells and compromising the lens circulation. The impairment of the lens circulation results in several changes, including the accumulation of Ca2+ in central lens regions, leading to the formation of precipitates that stain with Alizarin red. The cataract morphology and the distribution of Alizarin red-stained material are similar, suggesting that the cataracts result from biomineralization within the organ. In this review, we suggest that this may be a general process for the formation of cataracts of different etiologies.

Intercellular Conduction Optimizes Arterial Network Function and Conserves Blood Flow Homeostasis During Cerebrovascular Challenges

Objective: Cerebral arterial networks match blood flow delivery with neural activity. Neurovascular response begins with a stimulus and a focal change in vessel diameter, which by themselves is inconsequential to blood flow magnitude, until they spread and alter the contractile status of neighboring arterial segments. We sought to define the mechanisms underlying integrated vascular behavior and considered the role of intercellular electrical signaling in this phenomenon. Approach and Results: Electron microscopic and histochemical analysis revealed the structural coupling of cerebrovascular cells and the expression of gap junctional subunits at the cell interfaces, enabling intercellular signaling among vascular cells. Indeed, robust vasomotor conduction was detected in human and mice cerebral arteries after focal vessel stimulation: a response attributed to endothelial gap junctional communication, as its genetic alteration attenuated this behavior. Conducted responses were observed to ascend from the penetrating arterioles, influencing the contractile status of cortical surface vessels, in a simulated model of cerebral arterial network. Ascending responses recognized in vivo after whisker stimulation were significantly attenuated in mice with altered endothelial gap junctional signaling confirming that gap junctional communication drives integrated vessel responses. The diminishment in vascular communication also impaired the critical ability of the cerebral vasculature to maintain blood flow homeostasis and hence tissue viability after stroke. Conclusions: Our findings highlight the integral role of intercellular electrical signaling in transcribing focal stimuli into coordinated changes in cerebrovascular contractile activity and expose, a hitherto unknown mechanism for flow regulation after stroke.

Intercellular Conduction Optimizes Arterial Network Function and Conserves Blood Flow Homeostasis during Cerebrovascular Challenges

Cerebral arterial networks match blood flow delivery with neural activity. Neurovascular response begins with a stimulus and a focal change in vessel diameter, which by themselves is inconsequential to blood flow magnitude, until they spread and alter the contractile status of neighboring arterial segments. We sought to define the mechanisms underlying integrated vascular behavior and considered the role of intercellular electrical signalling in this phenomenon. Electron microscopic and histochemical analysis revealed the structural coupling of cerebrovascular cells and the expression of gap junctional subunits at the cell interfaces, enabling intercellular signaling among vascular cells. Indeed, robust vasomotor conduction was detected in human and mice cerebral arteries after focal vessel stimulation; a response attributed to endothelial gap junctional communication, as its genetic alteration attenuated this behavior. Conducted responses was observed to ascend from the penetrating arterioles, influencing the contractile status of cortical surface vessels, in a simulated model of cerebral arterial network. Ascending responses recognised in vivo after whisker stimulation, were significantly attenuated in mice with altered endothelial gap junctional signalling confirming that gap junctional communication drives integrated vessel responses. The diminishment in vascular communication also impaired the critical ability of the cerebral vasculature to maintain blood flow homeostasis and hence tissue viability, after stroke. Our findings establish the integral role of intercellular electrical signalling in transcribing focal stimuli into coordinated changes in cerebrovascular contractile activity and expose, a hitherto unknown mechanism for flow regulation after stroke.SignificanceNeurovascular responses are viewed as a one step process whereby stimuli derived from neural cells focally diffuse to a neighboring vessel, altering its contractile state. While focal changes in tone can subtly tune flow distribution, they can’t substantively change “perfusion magnitude” as vascular resistance is broadly distributed along the cerebral arterial tree. We report that nature overcomes this biophysical constraint by conducting electrical signals among coupled vascular cells, along vessels, and across branch points. Our quantitative exploration of intercellular conduction illustrates how network coordination optimizes blood flow delivery in support of brain function. Diminishing the ability of vascular cells to electrically communicate, mitigates the brain’s ability to regulate perfusion during functional hyperemia and after stroke, the latter advancing tissue injury.

76 Effects of serum type in maturation medium on in vitro development of bovine embryos

This study investigated the effect of bovine serum albumin (BSA), charcoal:dextran stripped fetal bovine serum (CDS FBS), and heat-inactivated FBS (HI FBS) in maturation medium on their ability to support in vitro oocyte maturation, cumulus cell-oocyte gap junctional communication, and development of bovine embryos. Charcoal:dextran treatment of FBS removes lipophilic chemicals, certain steroid hormones, and certain growth factors; however, HI FBS have a lot-to-lot variation in steroid hormones level that can affect the reproducibility of experimental findings. Oocytes were cultured in TCM-199 supplemented with either 8% (w/v) BSA, 10% (v/v) CDS FBS, or 10% (v/v) HI FBS and 1µg mL−1 oestradiol-17β, 10µg mL−1 FSH, 10ng mL−1 epidermal growth factor, 0.6mM cysteine, 0.2mM sodium pyruvate, and followed by IVF, and the zygotes were cultured in SOF-BE1 medium. The developmental ability and quality of bovine embryos were determined by assessing their cell number, lipid content, mitochondrial activity, gene expression, immunocytochemistry, and cryo-tolerance. The differences in embryo development between experimental groups were analysed by 1-way ANOVA. The Duncan’s multiple range tests were used to test the differences between the treatments. The level of statistical significance was set at P<0.05. We have shown that CDS FBS significantly improved (P<0.05) the percentage of MII oocytes compared with that in the BSA supplemented group (77.2±1.0% v. 69.3%±2.3%, respectively). Moreover, CDS FBS had a higher significant (P<0.05) effect on the rate of blastocyst formation compared with HI FBS and BSA (45.2±0.7% v. 37.4±1.5% and 31.1±3.9%, respectively; 6 replicates were performed). Culture of oocytes with CDS FBS increased (P<0.05) the expression of gap junction proteins, CX37 and CX43, at both transcriptional and translation levels as determined by quantitative RT-PCR and immunofluorescence analysis, respectively. We also found that CDS FBS significantly increased total cell number and decreased the apoptotic index in Day-8 blastocysts compared with the BSA group. Furthermore, the beneficial effects of CDS FBS on embryos were associated with significantly reduced intracellular lipid content and increased mitochondrial activity in both oocytes and blastocysts as identified by Nile red and MitoTracker Green staining, respectively. Taken together, these data suggest that supplementation of maturation medium with CDS FBS, as an alternative to HI FBS, affected cumulus cell-oocyte gap junctional communication, and subsequently improved in vitro developmental competence of bovine oocytes and embryos. Research was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries (IPET) through Agri-Bio industry Technology Development Program, funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA) (grant numbers: 117029-3 and 315017-5).