Analysis of Methamphetamine in Urine by HPLC with Solid-Phase Dispersive Extraction and Solid-Phase Fluorescence Derivatization.

We have developed a fluorescence detection-liquid chromatography (HPLC-FL) method that involves sample pretreatment by solid-phase dispersive extraction (SPDE) and solid-phase fluorescence derivatization for the simple and rapid analysis of methamphetamine (MA) in urine. This method uses a reversed-phase polymeric solid-phase gel to clean up analytes in SPDE, followed by fluorescence derivatization with 9-fluorenylmethyl chloroformate (FMOC) in the solid-phase. The optimal conditions for SPDE and solid-phase fluorescence derivatization were obtained when J-SPEC PEP was used as the solid-phase gel and 0.5 mmol/L FMOC in 50 mmol/L borate buffer solution (pH 10) was used as the fluorescence derivatization reagent. The recovery experiment of MA in urine yielded a clean chromatogram with no interfering peaks, demonstrating the validity of our method; the recoveries were 83.6% when spiked at a low concentration level (100 ng/mL) and 80.7% when spiked at a high concentration level (1000 ng/mL). Compared with the conventional liquid-phase method, the reaction product (FMOC-MA) of solid-phase fluorescence derivatization had higher stability. Reaction rate constants were calculated by changing the temperature conditions, and physicochemical parameters, including activation energy and activation entropy involved in the degradation reaction, were obtained from the Arrhenius plot and analyzed thermodynamically. Taken together, our results suggest that the HPLC-FL method with SPDE and solid-phase fluorescence derivatization for sample pretreatment provides a simple and rapid means of analyzing MA in urine samples.

Unique pH dynamics in GABAergic synaptic vesicles illuminates the mechanism and kinetics of GABA loading.

GABA acts as the major inhibitory neurotransmitter in the mammalian brain, shaping neuronal and circuit activity. For sustained synaptic transmission, synaptic vesicles (SVs) are required to be recycled and refilled with neurotransmitters using an H(+) electrochemical gradient. However, neither the mechanism underlying vesicular GABA uptake nor the kinetics of GABA loading in living neurons have been fully elucidated. To characterize the process of GABA uptake into SVs in functional synapses, we monitored luminal pH of GABAergic SVs separately from that of excitatory glutamatergic SVs in cultured hippocampal neurons. By using a pH sensor optimal for the SV lumen, we found that GABAergic SVs exhibited an unexpectedly higher resting pH (∼6.4) than glutamatergic SVs (pH ∼5.8). Moreover, unlike glutamatergic SVs, GABAergic SVs displayed unique pH dynamics after endocytosis that involved initial overacidification and subsequent alkalization that restored their resting pH. GABAergic SVs that lacked the vesicular GABA transporter (VGAT) did not show the pH overshoot and acidified further to ∼6.0. Comparison of luminal pH dynamics in the presence or absence of VGAT showed that VGAT operates as a GABA/H(+) exchanger, which is continuously required to offset GABA leakage. Furthermore, the kinetics of GABA transport was slower (τ > 20 s at physiological temperature) than that of glutamate uptake and may exceed the time required for reuse of exocytosed SVs, allowing reuse of incompletely filled vesicles in the presence of high demand for inhibitory transmission.

Monitoring of vacuolar-type H+ ATPase-mediated proton influx into synaptic vesicles.

During synaptic vesicle (SV) recycling, the vacuolar-type H(+) ATPase creates a proton electrochemical gradient (ΔµH(+)) that drives neurotransmitter loading into SVs. Given the low estimates of free luminal protons, it has been envisioned that the influx of a limited number of protons suffices to establish ΔµH(+). Consistent with this, the time constant of SV re-acidification was reported to be <5 s, much faster than glutamate loading (τ of ∼ 15 s) and thus unlikely to be rate limiting for neurotransmitter loading. However, such estimates have relied on pHluorin-based probes that lack sensitivity in the lower luminal pH range. Here, we reexamined re-acidification kinetics using the mOrange2-based probe that should report the SV pH more accurately. In recordings from cultured mouse hippocampal neurons, we found that re-acidification took substantially longer (τ of ∼ 15 s) than estimated previously. In addition, we found that the SV lumen exhibited a large buffering capacity (∼ 57 mm/pH), corresponding to an accumulation of ∼ 1200 protons during re-acidification. Together, our results uncover hitherto unrecognized robust proton influx and storage in SVs that can restrict the rate of neurotransmitter refilling.

Cyclical dermal micro-niche switching governs the morphological infradian rhythm of mouse zigzag hair.

Biological rhythms are involved in almost all types of biological processes, not only physiological processes but also morphogenesis. Currently, how periodic morphological patterns of tissues/organs in multicellular organisms form is not fully understood. Here, using mouse zigzag hair, which has 3 bends, we found that a change in the combination of hair progenitors and their micro-niche and subsequent bend formation occur every three days. Chimeric loss-of-function and gain-of-function of Ptn and Aff3, which are upregulated immediately before bend formation, resulted in defects in the downward movement of the micro-niche and the rhythm of bend formation in an in vivo hair reconstitution assay. Our study demonstrates the periodic change in the combination between progenitors and micro-niche, which is vital for the unique infradian rhythm.