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HL‐1 cells are adult mouse atrial myocytes induced to proliferate indefinitely by SV40 large T antigen. These cells beat spontaneously when confluent and express several adult cardiac cell markers including the outward delayed rectifier K+ channel. Here, we examined the presence of a hyperpolarization‐activated If current in HL‐1 cells using the whole‐cell patch‐clamp technique on isolated cells enzymatically dissociated from the culture at confluence. Cell membrane capacitance (Cm) ranged from 5 to 53 pF. If was detected in about 30 % of the cells and its occurrence was independent of the stage of the culture. If maximal slope conductance was 89.7 ± 0.4 pS pF−1 (n= 10). If current in HL‐1 cells showed typical characteristics of native cardiac If current: activation threshold between −50 and −60 mV, half‐maximal activation potential of −83.1 ± 0.7 mV (n= 50), reversal potential at −20.8 ± 1.5 mV (n= 10), time‐dependent activation by hyperpolarization and blockade by 4 mm Cs+. In half of the cells tested, activation of adenylyl cyclase by the forskolin analogue L858051 (20 μm) induced both a ≈6 mV positive shift of the half‐activation potential and a ≈37 % increase in the fully activated If current. RT‐PCR analysis of the hyperpolarization‐activated, cyclic nucleotide‐gated channels (HCN) expressed in HL‐1 cells demonstrated major contributions of HCN1 and HCN2 channel isoforms to If current. Cytosolic Ca2+ oscillations in spontaneously beating HL‐1 cells were measured in Fluo‐3 AM‐loaded cells using a fast‐scanning confocal microscope. The oscillation frequency ranged from 1.3 to 5 Hz and the spontaneous activity was stopped in the presence of 4 mm Cs+. Action potentials from HL‐1 cells had a triangular shape, with an overshoot at +15 mV and a maximal diastolic potential of −69 mV, i.e. more negative than the threshold potential for If activation. In conclusion, HL‐1 cells display a hyperpolarization‐activated If current which might contribute to the spontaneous contractile activity of these cells.

We report a novel method of engineering a highly effective collagen-cell scaffold based on RGD+ peptides cross-linked to a clinically approved collagen matrix. The main advantages were cell contractile performance, cardiomyocyte viability and differentiation.

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Adenomatous polyposis coli (Apc) is a cell polarity regulator and a tumor suppressor associated with familial adenomatous polyposis and colorectal cancer. Apc involvement in T lymphocyte functions and antitumor immunity remains poorly understood. Investigating Apc-depleted human CD8 T cells and CD8 T cells from Apc Min/+ mutant mice, we found that Apc regulates actin and microtubule cytoskeleton remodeling at the immunological synapse, controlling synapse morphology and stability and lytic granule dynamics, including targeting and fusion at the synapse. Ultimately, Apc tunes cytotoxic T cell activity, leading to tumor cell killing. Furthermore, Apc modulates early TCR signaling and nuclear translocation of the NFAT transcription factor with mild consequences on the expression of some differentiation markers. In contrast, no differences in the production of effector cytokines were observed. These results, together with our previous findings on Apc function in regulatory T cells, indicate that Apc mutations may cause a dual damage, first unbalancing epithelial cell differentiation and growth driving epithelial neoplasms and, second, impairing T cell-mediated antitumor immunity at several levels. ImmunoHorizons, 2020, 4: 363-381.

Background: Interleukin-7 is the master regulator of T-cell proliferation. Results: IL-7 drives its receptor in a membrane microdomain that regulates phosphorylation of associated tyrosine kinases JAK1 and JAK3, anchors IL-7 receptor to cytoskeleton and regulates STAT5 phosphorylation and nuclear translocation. Conclusion: Membrane microdomains and cytoskeleton scaffold IL-7R-signalosomes and assist signaling protein transport. Significance: Transient membrane and cytoskeleton organization shapes IL-7-signaling mechanisms in CD4 T-cells.

The distribution of delta opioid receptors, selectively labelled in vitro with the photoaffinity probe monoiodo azido-DTLET ([D-Thr2,pN3Phe4, Leu5]enkephaly-Thr6), was analyzed by light and electron microscopic radioautography in sections from rat neostriatum. Preliminary experiments indicated that up to 65% of specific 125I-azido-DTLET binding to rat striatal sections was still detectable following prefixation of the brain with 0.5% glutaraldehyde. These experiments also showed that up to 20-30% of the specifically bound radioactivity was covalently linked following ultraviolet irradiation and was thereby retained in tissue during subsequent postfixation and dehydration steps. Accordingly, the topographic distribution of the covalently attached azido-DTLET molecules was similar to that seen in fresh frozen sections and characteristic of that previously described for delta sites. Light and electron microscopic examination of the label in prefixed, striatal sections irradiated with ultraviolet light revealed that a significant proportion of specifically bound 125I-azido-DTLET molecules was intraneuronal. Specifically, 16% of the labelled binding sites were found in dendrites, 12% in perikarya and 4% in axon terminals. These results suggest that an important proportion of delta opioid binding sites labelled in the neostriatum correspond to receptors that are undergoing synthesis, transport and/or recycling. They also imply that a major fraction of delta sites are associated with intrastriatal neurons, as opposed to afferent axons. Approximately 44% of the labelled binding sites were associated with neuronal plasma membranes. Although most of these were found at the level of axodendritic (20%) and dendrodendritic (7%) appositions, comparison of the labelling incidence of these two compartments with their frequency of occurrence in tissue suggested that delta sites are fairly widely dispersed along neuronal plasma membranes. Only a small proportion (smaller than that of mu or kappa sites labelled in the same region) was associated with synaptic specializations. These results support the concept that delta receptors correspond to molecular entities that are distinct from mu and kappa sites and suggest that delta ligands act primarily nonjunctionally on the plasma membrane of striatal neurons.