Hyperkalemic periodic paralysis and the adult muscle sodium channel alpha-subunit gene

Hyperkalemic periodic paralysis (HYPP) is an autosomal dominant disorder characterized by episodes of muscle weakness due to depolarization of the muscle cell membrane associated with elevated serum potassium. Electrophysiological studies have implicated the adult muscle sodium channel. Here, portions of the adult muscle sodium channel alpha-subunit gene were cloned and mapped near the human growth hormone locus (GH1) on chromosome 17. In a large pedigree displaying HYPP with myotonia, these two loci showed tight linkage to the genetic defect with no recombinants detected. Thus, it is likely that the sodium channel alpha-subunit gene contains the HYPP mutation.     

The effect of vitamin a supplementation on seminal characteristics and vitamin a absorption in stallions

Fourteen mature stallions were paired based on age and pretreatment spermatozoal output. One member of each pair was assigned to either 1) control (3 ml corn oil) or 2) treated (132,000 IU retinyl palmitate in 3 ml corn oil) experimental groups. Treatments were added to oat rations every other day. Seminal characteristics (gel free volume, gel volume, total seminal volume, percent progressively motile spermatozoa, number of spermatozoa per ml, percentage morphologically normal spermatozoa and spermatozoal membrane stability) and total scrotal width of each stallion were recorded before (February) and after three months of vitamin A supplementation (June). Plasma vitamin A was measured at 0,6,12,24, and 48 hours following the first and last treatments to document absorption. There were no treatment effects (p>.05) on seminal characteristics or scrotal width. Seasonal increases were recorded in gel-free volume, total seminal volume, percent spermatozoal motility, total spermatozoal output, percentage of morphologically normal spermatozoa, and total scrotal width. Plasma vitamin A was lower during the second collection period (June) than the first (February) in both treatment groups. Peak plasma vitamin A was observed 48 hours following ingestion of the first dose of the vitamin but at 12 hours following the last treatment.     

Clindamycin-resistance in methicillin-resistant Staphylococcus aureus isolated from animals

Clindamycin is widely used in veterinary medicine to treat a variety of bacterial infections. Resistance to clindamycin amongst staphylococci may be due to modification of the ribosomal target site. Resistance due to this mechanism is encoded by the erm genes, which may be either constitutively or inducibly expressed. Inducible expression of resistance is not usually demonstrable by routine laboratory susceptibility testing, however, a relatively simple double disc agar diffusion test (D-test) may be used to detect the presence of inducible resistance. Two hundred and eighty-five isolates of methicillin-resistant Staphylococcus aureus (MRSA) isolated from infections in animals were tested using the D-test for the presence of inducible clindamycin resistance. One hundred and seven (71%) of the strains tested demonstrated inducible resistance to clindamycin, which were not detected on initial susceptibility testing. It has been shown that there is potential for staphylococci to develop resistance to clindamycin whilst on treatment when inducible resistance mechanisms are present. Therefore, routine screening for inducible resistance may be prudent.     

Fat digestibility in Equus caballus follows increasing first-order kinetics

The digestibility of ether extract varies greatly from forages to grains and further to added fats consisting mainly of triglycerides. This variation has been attributed to two main factors, the presence of nonhydrolyzable substances in the ether extract, especially in leafy foods, and the dilution of endogenous fecal fat. A compilation of results from 188 equine digestion balance observations on five basal feeds and 18 test feeds with added fats demonstrated a true digestibility of fat approaching 100% and an endogenous fecal fat of 0.22 g x d(-1) x kg BW(-1). The results revealed that nonhydrolyzable ether extract and endogenous fecal fat were insufficient to account for the difference between true digestibility and apparent digestibilities of ether extract in basal feeds and partial digestibilities of added fats in test feeds. A third possible contributing factor was demonstrated: an increasing first-order relationship between observed digestibilities (D, %) and the fat content of the feed (F, g/kg): D = 92.0 - 92.0e(-F/342). r2 = 0.81, P < 0.001. This equation indicates that 46% digestibility (half maximum) occurs at an ether extract or fat content of 24 g/kg, which is common in forages. It is consistent with fat digestibility or efficiency of absorption being a function of the rate of lipolysis, especially when residence time in the small intestine is limited. Consequently, we suggest that the kinetics of lipases, which are difficult to measure, may contribute to low digestibility when substrate concentration in the small intestine is low due to a low fat content in food. The status of vitamins A and E might be affected by low dietary fat contents and might be improved by fat supplementation.     

Tim50 maintains the permeability barrier of the mitochondrial inner membrane

Transport of metabolites across the mitochondrial inner membrane is highly selective, thereby maintaining the electrochemical proton gradient that functions as the main driving force for cellular adenosine triphosphate synthesis. Mitochondria import many preproteins via the presequence translocase of the inner membrane. However, the reconstituted Tim23 protein constitutes a pore remaining mainly in its open form, a state that would be deleterious in organello. We found that the intermembrane space domain of Tim50 induced the Tim23 channel to close. Presequences overcame this effect and activated the channel for translocation. Thus, the hydrophilic cis domain of Tim50 maintains the permeability barrier of mitochondria by closing the translocation pore in a presequence-regulated manner.