Assignment of the porcine major histocompatibility complex to chromosome 7 by in situ hybridization

The major histocompatibility complex (SLA) of the domestic pig (Sus scrofa) was regionally mapped to 7p12----q12 by in situ hybridization with an SLA class I-specific recombinant DNA probe. This localization contradicts linkage data suggesting a possible assignment of the SLA locus to porcine chromosome 15.     

Large-conductance Ca2+-activated K+ channels in freshly dissociated smooth muscle cells

Freshly dissociated cells from the stomach muscularis of the toad Bufo marinus have been employed to carry out a systematic set of electrophysiological studies on the membrane properties of smooth muscle. The existence of Ca2+-activated K+ channels became apparent during the first studies under current clamp. In subsequent studies under voltage clamp, a Ca2+-activated. TEA-sensitive outward current was evident, and it was more than an order of magnitude larger than any other current observed in the cells. The channel responsible, at least in part, for this large outward current has been identified on the basis of single-channel records, and some of its main characteristics have been studied. It is similar in many respects to the large-conductance, Ca2+-activated K+ channel seen in other preparations. This channel has now been found in a considerable diversity of smooth muscle types.     

Interactions of the neurotoxic amine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine with monoamine oxidases.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a thermal breakdown product of a meperidine-like narcotic used by drug abusers as a heroin substitute, produces Parkinsonian symptoms in humans and primates. The nigrostriatal toxicity is not due to MPTP itself but to one or more oxidation products resulting from the action of monoamine oxidase (MAO) on this tertiary allylamine. Both MAO A and B catalyse the oxidation of MPTP to the 1-methyl-4-phenyl-2,3-dihydropyridinium species (MPDP+), which undergoes further oxidation to the fully aromatic 1-methyl-4-phenylpyridinium species (MPP+). These bio-oxidations are blocked by selective inhibitors of MAO A and B. Additionally, MPTP, MPDP+ and MPP+ are competitive inhibitors of MAO A and B. The A form of the enzyme is particularly sensitive to this type of reversible inhibition. Both MAO A and B also are irreversibly inactivated by MPTP and MPDP+, but not by MPP+. This inactivation obeys the characteristics of a mechanism-based or 'suicide' process. The inactivation, which is accompanied by the incorporation of radioactivity from methyl-labelled MPTP, is likely to result from covalent modification of the enzyme.     

In vivo metabolic intermediates of phospholipid biosynthesis in Rhodopseudomonas sphaeroides

The in vivo metabolic pathways of phospholipid biosynthesis in Rhodopseudomonas sphaeroides have been investigated. Rapid pulse-chase-labeling studies indicated that phosphatidylethanolamine and phosphatidylglycerol were synthesized as in other eubacteria. The labeling pattern observed for N-acylphosphatidylserine (NAPS) was inconsistent with the synthesis of this phospholipid occurring by direct acylation of phosphatidylserine (PS). Rather, NAPS appeared to be kinetically derived from an earlier intermediate such as phosphatidic acid or more likely CDP-diglyceride. Tris-induced NAPS accumulation specifically reduced the synthesis of PS. Treatment of cells with a bacteriostatic concentration of hydroxylamine (10 mM) greatly reduced total cellular phospholipid synthesis, resulted in accumulation of PS, and stimulated the phosphatidylglycerol branch of phospholipid metabolism relative to the PS branch of the pathway. When the cells were treated with a lower hydroxylamine dosage (50 microM), total phospholipid synthesis lagged as PS accumulated, however, phospholipid synthesis resumed coincident with a reversal of PS accumulation. Hydroxylamine alone was not sufficient to promote NAPS accumulation but this compound allowed continued NAPS accumulation when cells were grown in medium containing Tris. The significance of these observations is discussed in terms of NAPS biosynthesis being representative of a previously undescribed branch of the phospholipid biosynthetic sequence.     

Immunoelectron microscopic studies of desmin (skeletin) localization and intermediate filament organization in chicken cardiac muscle

We studied the localization of desmin (skeletin), the major protein subunit of muscle-type intermediate filaments, in adult chicken cardiac muscle by high resolution immunoelectron microscopic labeling of ultrathin frozen sections of the intact fixed tissues. We carried out single labeling for desmin and double labeling for both desmin and either vinculin or alpha-actinin. In areas removed from the intercalated disk membranes, we observed desmin labeling between adjacent Z-bands in every interfibrillar space. Where these spaces were wide and contained mitochondria, convoluted strands of desmin labeling bridged between the periphery of neighboring Z-bands and the mitochondria. The intermediate filaments appeared to be organized in a more three-dimensional manner within the interfibrillar spaces of cardiac as compared to skeletal muscle. Near the intercalated disks, desmin labeling was intense within the interfibrillar spaces, but was completely segregated from the microfilament attachment sites (fascia adherens) where vinculin and alpha-actinin were localized. Desmin therefore appears to play no role in the attachment of microfilaments to the intercalated disk membrane. We discuss the role of intermediate filaments in the organization of cardiac and skeletal striated muscle in the light of these and other results.