Therapeutic intervention for human succinic semialdehyde dehydrogenase (SSADH) deficiency (␥-hydroxybutyric aciduria) has been limited to vigabatrin (VGB). Pharmacologically, VGB should be highly effective due to 4-aminobutyrate-transaminase (GABA-transaminase) inhibition, lowering succinic semialdehyde and, thereby, ␥-hydroxybutyric acid (GHB) levels. Unfortunately, clinical efficacy has been limited. Because GHB possesses a number of potential receptor interactions, we addressed the hypothesis that antagonism of these interactions in mice with SSADH deficiency could lead to the development of novel treatment strategies for human patients. SSADH-deficient mice have significantly elevated tissue GHB levels, are neurologically impaired, and die within 4 weeks postnatally. In the current report, we compared oral versus intraperitoneal administration of VGB, CGP 35348 [3-aminopropyl(diethoxymethyl)phosphinic acid, a GABA B receptor antagonist], and the nonprotein amino acid taurine in rescue of SSADH-deficient mice from early death. In addition, we assessed the efficacy of the specific GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-[H]benzocycloheptene-5-ol-6-ylideneacetic acid) using i.p. administration. All interventions led to significant lifespan extension (22-61%), with NCS-382 being most effective (50 -61% survival). To explore the limited human clinical efficacy of VGB, we measured brain GHB and ␥-aminobutyric acid (GABA) levels in SSADH-deficient mice receiving VGB. Whereas high-dose VGB led to the expected elevation of brain GABA, we found no parallel decrease in GHB levels. Our data indicate that, at a minimum, GHB and GABA B receptors are involved in the pathophysiology of SSADH deficiency. We conclude that taurine and NCS-382 may have therapeutic relevance in human SSADH deficiency and that the poor clinical efficacy of VGB in this disease may relate to an inability to decrease brain GHB concentrations.

We examined the role of the Ca2+‐regulated protein phosphatase calcineurin in controlling Ca2+ signalling in mouse ventricular myocytes. Membrane currents and voltage were measured in single myocytes using the patch‐clamp technique. Cytoplasmic Ca2+ concentration ([Ca2+]i) was measured in cells loaded with the fluorescent Ca2+ indicators fluo‐4 or fura‐2 using a confocal or epifluorescence microscope. Inhibition of calcineurin with cyclosporin A (CsA, 100 nm) or the calcineurin auto‐inhibitory peptide (CiP, 100 μM), increased the amplitude and rate of decay of the evoked [Ca2+]i transient and also prolonged the action potential (AP) of ventricular myocytes to a similar extent. The effects of CsA (100 nm) and 100 μM CiP on the [Ca2+]i transient and AP were not additive. Calcineurin inhibition did not modify the K+ currents responsible for repolarisation of the mouse ventricle. Instead, inhibition of calcineurin increased the amplitude of the Ca2+ current (ICa) and the evoked calcium transient normalized to the ICa. Calcium sparks, which underlie the [Ca2+]i transient, had a higher frequency and amplitude, suggesting an elevation of SR calcium load. Inhibition of protein kinase A (PKA) prevented the effects of calcineurin inhibition, indicating that calcineurin opposes the actions of PKA. Finally, immunofluorescence images suggest that calcineurin and PKA co‐localize near the T‐tubules of ventricular myocytes. We propose that calcineurin and PKA are co‐localized to control Ca2+ influx through calcium channels and calcium release through ryanodine receptors.

In the scanning electron microscope, the surface of wool fibers is much rougher than that of mohair or other specialty fibers, mainly due to differences in the frequency and height of the cuticle scales. In order to assess and quantify these differences, which are essential for the perception of "roughness" and thus for fast fiber discrimination, mechan ical profilometry is used to assess coarse Merino wool and Texas mohair fibers. The data are analyzed by smoothing and Fourier analysis to separate cuticle-related effects of roughness from longer term fiber diameter changes attributed mainly to the characteristic circadian (daily) biological rhythm of the animal. The results show that subjectively observed differences in the roughness of the two fiber types are reflected in roughness and frequency parameters obtained from their mechanical profiles, enabling reliable discrim ination between wool and mohair.

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