An invertebrate model in examining the effect of acute ferric iron exposure on proprioceptive neurons

Iron is an essential element for plant and animal life and is found in soil, fresh waters and marine waters. The Fe³⁺ ion is a vital prosthetic group and cofactor to mitochondrial electron transport complexes and numerous proteins involved in normal functioning. Despite its importance to life-sustaining processes, overexposure results in toxicity. For example, ferric iron (Fe³⁺) accumulation in the mammalian central nervous system is associated with various neurological disorders. Although current literature addresses the long-term effects of Fe³⁺ overload, fewer studies exist examining the effects of acute exposure. Using the blue crab (Callinectes sapidus), we investigate the effects of acute Fe³⁺ overload on proprioception within the propodite-dactylopodite (PD) nerve. For proprioceptive studies, 10- and 20-mM ferric chloride and ferric ammonium citrate solutions were used at 5- and 20- min exposure times. Exposure to 20 mM concentrations of ferric chloride and ferric ammonium citrate reduced excitability in proprioceptive neurons. Thus, Fe³⁺ likely blocks stretch-activated channels or voltage-gated Na⁺ channels. The depressive effects of Fe³⁺ are partly reversible following saline washout, indicating cells are not acutely damaged. Gadolinium (GdCl₃, 1 and 10 mM) was used to examine the effects of an additional trivalent ion comparator. Gd³⁺ depressed PD nerve compound action potential amplitude while increasing the compound action potential duration. This study is relevant in demonstrating the dose-dependent effects of acute Fe³⁺ and Gd³⁺ exposure on proprioception and provides a model system to further investigate the mechanisms by which metals act on the nervous system.

Delineating Ultrafast Structural Dynamics of a Green-Red Fluorescent Protein for Calcium Sensing

Fluorescent proteins (FPs) are indispensable tools for noninvasive bioimaging and sensing. Measuring the free cellular calcium (Ca²⁺) concentrations in vivo with genetically encodable FPs can be a relatively direct measure of neuronal activity due to the complex signaling role of these ions. REX-GECO1 is a recently developed red-green emission and excitation ratiometric FP-based biosensor that achieves a high dynamic range due to differences in the chromophore response to light excitation with and without calcium ions. Using steady-state electronic measurements (UV/Visible absorption and emission), along with time-resolved spectroscopic techniques including femtosecond transient absorption (fs-TA) and femtosecond stimulated Raman spectroscopy (FSRS), the potential energy surfaces of these unique biosensors are unveiled with vivid details. The ground-state structural characterization of the Ca²⁺-free biosensor via FSRS reveals a more spacious protein pocket that allows the chromophore to efficiently twist and reach a dark state. In contrast, the more compressed cavity within the Ca²⁺-bound biosensor results in a more heterogeneous distribution of chromophore populations that results in multi-step excited state proton transfer (ESPT) pathways on the sub-140 fs, 600 fs, and 3 ps timescales. These results enable rational design strategies to enlarge the spectral separation between the protonated/deprotonated forms and the Stokes shift leading to a larger dynamic range and potentially higher fluorescence quantum yield, which should be broadly applicable to the calcium imaging and biosensor communities.

Molecular physiology of manganese in insects

Manganese is an essential element for maintaining life. Overexposure to the metal, however, can be toxic to organisms. Given the significant function of manganese in insects, agriculture, and human disease, as well as in the healthy ecology of the planet, the biological activities of manganese in insects needs consideration. Because of the role of manganese as a cofactor for essential enzymes present in different organelles, both over and underexposure to manganese has a multifaceted effect on organisms. At the physiological level, the effects of insect exposure to the metal on enzymatic activities and consequent alteration of insect behaviors are best explained through the metal's role in modulating the dopaminergic system. Despite numerous examples that alterations in manganese homeostasis have profound effects on insects, the cellular mechanisms that ensure homeostasis of this essential metal remain presently unknown, calling for further research in this area.