Role of the vestibular nuclei in endothelin-1-induced barrel rotation in rats

The Evidence for Sparsentan-Mediated Inhibition of INa and IK(erg): Possibly Unlinked to Its Antagonism of Angiotensin II or Endothelin Type a Receptor

Sparsentan is viewed as a dual antagonist of endothelin type A (ET_A) receptor and angiotensin II (AngII) receptor and it could be beneficial in patients with focal segmental glomerulosclerosis. Moreover, it could improve glomerular filtration rate and augment protective tissue remodeling in mouse models of focal segmental glomerulosclerosis. The ionic mechanisms through which it interacts with the magnitude and/or gating kinetics of ionic currents in excitable cells were not thoroughly investigated. Herein, we aimed to examine the effects of varying sparsentan concentrations on ionic currents residing in pituitary GH₃ somatolactotrophs. From whole-cell current recordings made in GH₃ cells, sparsentan (0.3–100 μM) differentially inhibited the peak and late components of voltage-gated Na⁺ current (I_Na). The IC₅₀ value of sparsentan required to exert a reduction in peak and late I_Na in GH₃ cells was 15.04 and 1.21 μM, respectively; meanwhile, the K_D value estimated from its shortening in the slow component of I_Na inactivation time constant was 2.09 μM. The sparsentan (10 μM) presence did not change the overall current–voltage relationship of I_Na; however, the steady-state inactivation curve of the current was shifted to more negative potential in its presence (10 μM), with no change in the gating charge of the curve. The window I_Na activated by a brief upsloping ramp was decreased during exposure to sparsentan (10 μM); moreover, recovery of peak I_Na became slowed in its presence. The Tefluthrin (Tef)-stimulated resurgent I_Na activated in response to abrupt depolarization followed by the descending ramp pulse was additionally attenuated by subsequent application of sparsentan. In continued presence of Tef (3 μM) or β-pompilidotoxin (3 μM), further application of sparsentan (3 μM) reversed their stimulation of I_Na. However, sparsentan-induced inhibition of I_Na failed to be overcome by subsequent application of either endothelin 1 (1 μM) or angiotensin II (1 μM); moreover, in continued presence of endothelin (1 μM) or angiotensin II (1 μM), further addition of sparsentan (3 μM) effectively decreased peak I_Na. Additionally, the application of sparsentan (3 μM) inhibited the peak and late components of erg-mediated K⁺ current in GH₃ cells, although it mildly decreased the amplitude of delayed-rectifier K⁺ current. Altogether, this study provides a distinct yet unidentified finding that sparsentan may perturb the amplitude or gating of varying ionic currents in excitable cells.

Contactin-associated protein (Caspr) 2 interacts with carboxypeptidase E in the CNS

To identify proteins interacting with the intracellular domain of the neural cell adhesion molecule contactin-associated protein 2 (Caspr2), yeast two-hybrid screening was performed. We identified carboxypeptidase E (CPE) as a Caspr2-interacting candidate protein. Glutathione S-transferase pull-down and immunoprecipitation analyses indicated that Caspr2 was associated with CPE in vitro and in vivo. Both Caspr2 and CPE were expressed predominantly in the CNS. Immunohistochemical analyses revealed that both Caspr2- and CPE-like immunoreactivities were found to co-localize in the apical dendrites and cell bodies of rat cortical neurons. In subcellular localization analysis, Caspr2- and CPE-like immunoreactivities were co-migrated in the fractions of Golgi/ER. Additionally, in COS-7 cells co-transfected with CPE and Caspr2 cDNAs, Caspr2- and CPE-immunoreactivities were co-localized in both Golgi and membrane, whereas it was only observed in Golgi of either COS-7 cell transfected with CPE or Caspr2 cDNA alone. It is known that the membrane-bound form of CPE functions as a sorting receptor of prohormones in the trans-Golgi network. Taken together, our data suggest that CPE may be a key molecule to regulate Caspr2 trafficking to the cell membrane.

Up-regulation of matrix metalloproteinase-3 in the dorsal root ganglion of rats with paclitaxel-induced neuropathy

Paclitaxel-induced painful peripheral neuropathy is a major dose-limiting factor. Recently, it has been reported that macrophages accumulated in the dorsal root ganglion of paclitaxel-treated rats, and their activation is suggested to contribute to generation and development of the neuropathy. However, the mechanism for macrophage activation is still unknown. In this study, to explore candidate genes involved in the mechanism for macrophage activation in the dorsal root ganglion of paclitaxel-treated rats, we developed model rats for paclitaxel-induced neuropathic pain and performed a microarray assay to analyze the changes of gene expressions in the dorsal root ganglion. Among the genes with changed expression levels, we focused on matrix metalloproteinase-3 (MMP-3, stromelysin-1) and CD163, a macrophage marker. By reverse transcription-polymerase chain reaction, the expression levels of MMP-3 and CD163 were markedly up-regulated in paclitaxel-treated dorsal root ganglion. As a result of immunohistochemical study, large ganglion neurons, but neither Schwann cells nor macrophages, predominantly expressed MMP-3. This MMP-3 up-regulation occurred prior to macrophage accumulation in the dorsal root ganglion. In addition, recombinant MMP-3 led to the activation of RAW264 macrophages in vitro. Taken together, the up-regulation of MMP-3 and following macrophage activation caused in the dorsal root ganglion might be a significant event to trigger a series of reactions developing paclitaxel-induced peripheral neuropathic pain.