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Abstract  Recent investigations suggest that the effects of neural agrin might not be limited to neuromuscular junction formation and maintenance and that other aspects of muscle development might be promoted by agrin. Here we tested the hypothesis that agrin induces a change in the excitability properties in primary cultures of non-innervated human myotubes. Electrical membrane properties of human myotubes were recorded using the whole-cell patch-clamp technique. Cell incubation with recombinant chick neural agrin (1 nM) led to a more negative membrane resting potential. Addition of strophanthidin, a blocker of the Na+/K+ ATPase, depolarized agrin-treated myotubes stronger than control, indicating, in the presence of agrin, a higher contribution of the Na+/K+ ATPase in establishing the resting membrane potential. Indeed, larger amounts of both the α1 and the α2 isoforms of the Na+/K+ ATPase protein were expressed in agrin-treated cells. A slight but significant down-regulation of functional apamin-sensitive K+ channels was observed after agrin treatment. These results indicate that neural agrin might act as a trophic factor promoting the maturation of membrane electrical properties during differentiation, confirming the role of agrin as a general promoter of muscle development. [ABSTRACT FROM AUTHOR]

This paper reports on the analysis of the toxin content from Palythoa tuberculosaand Palythoa toxicasamples collected off of the Hawaiian coast. Our work, based on in-depth high-resolution liquid chromatography−mass spectrometry analysis along with extensive NMR study, led us to structurally characterize 42-hydroxy-palytoxin, a new palytoxin congener. This toxin and palytoxin itself appeared to be the major components of toxic extract from a P. tuberculosasample, while 42-hydroxy-palytoxin was proven by far to be the main palytoxin derivative in P. toxica. Functional studies on this new palytoxin-like compound suggest that the new palytoxin analogue and palytoxin itself present similar biological activities. [ABSTRACT FROM AUTHOR]

Oral administration of yessotoxin (YTX) has been reported to induce ultrastructural alterations in rodent cardiac muscle. To study its effects on various fundamental aspects of cardiac muscle cells activity, that is, cell beating, Ca2+ and cyclic adenosine 3′,5′-monophosphate (cAMP) levels, as well as cell vitality, a primary culture of rat cardiomyocytes was used. Patch-clamp recordings, Ca2+ imaging, and cAMP assays were performed on cultured cardiomyocytes to characterize YTX effects on the cell beating frequency. 3-(4,5-Dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) and sulforhodamine B (SRB) tests were carried out to determine its effect on cardiomyocytes viability. Videoimaging techniques showed a time- and concentration-dependent reduction in the beating frequency after 1, 5, and 24 h incubation with YTX (0.1−1μM). This effect was neither associated to the uncoupling between the membrane electrical activity and Ca2+ release from intracellular stores nor to the impairment of the mechanisms controlling the Ca2+ homeostasis. In addition, 1μM YTX did not modify basal cAMP levels in cardiomyocytes. MTT and SRB assays revealed that incubation of cardiomyocytes with YTX (0.01−1μM; 24, 48, and 72 h) caused a decrease in cell viability in a concentration- and time-dependent way. This effect was still evident in cardiomyocytes exposed to YTX for 1, 5, and 24 h and cultured up to 72 h in YTX-free medium. Our results demonstrate that, at nanomolar concentrations, a short incubation with YTX causes an inhibition of the beating activity and an irreversible reduction of viability of cardiac cells in vitro. [ABSTRACT FROM AUTHOR]