PubMed · 8753591
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H Shuto, K Otsubo. 1995. [Zonisamide].. https://pubmed.ncbi.nlm.nih.gov/8753591/
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The gamma-aminobutyric acid (GABA) response profiles of IMR-32 human neuroblastoma cells were examined using whole-cell patch clamp and RT-PCR techniques. GABA activated a concentration-dependent and bicuculline-sensitive current, and RT-PCR revealed the expression of multiple GABA(A) receptor subunit mRNAs (alpha(1), alpha(3), alpha(4), beta(1), beta(3), gamma(2), and delta). A pharmacological profile of the GABA-induced current was derived using several subunit-selective agents. Diazepam, which requires the presence of a gamma subunit in order to modulate GABA(A) receptor-mediated responses, potentiated GABA-induced currents in a subset of IMR-32 cells. Two populations of GABA-activated currents were also evident based on sensitivity to modulation by zinc. Comparison of zinc- and diazepam-induced modulation of GABA-induced current responses in the same cells revealed an inverse correlation between these two modulators. No differences, however, were observed with the GABA(A) receptor modulators loreclezole, allopregnanolone, and pentobarbital. Thus, IMR-32 cells maintained in culture are heterogeneous in terms of expression of GABA(A) receptor isoforms.
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The influence of egg albumin (EA) on the crystal habit properties of carbamazepine (CBZ) in aqueous solutions, solid-state, and in sustained release matrix tablets was investigated using differential scanning calorimetry (DSC), hot-stage microscopy (HSM), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and contact angle goniometer (CAG). The results suggest that in solid-state mixtures, EA affected the polymorphic transitions of CBZ from the beta to the alpha form. In hydrated matrix tablets and aqueous solutions, EA influenced the conversion rate of CBZ to the dihydrate form depending on EA concentration. It was found that increasing EA concentration enhanced CBZ dihydrate aggregation, an effect that leads to the formation of crystals with high mechanical strength and decrease of CBZ solubility. Possible mechanisms, which explain crystal growth and aggregation, as well as alteration of CBZ polymorphic transitions in the solid-state, gel layer, and in aqueous solution were suggested. In the gel layer of hydrated tablets the kinetics of CBZ transformation to the dihydrate form, crystal growth and aggregation were influenced by various processes: matrix hydration, erosion mechanism and the formation of metastable conditions, which favor aggregation and growth. The release kinetics of CBZ from the matrix highly correlated with the crystalline and morphological changes occurring in the matrix.