Pacemaker Potentials for the Periodic Burst Discharge in the Heart Ganglion of a Stomatopod, Squilla oratoria

From somata of the pacemaker neurons in the Squilla heart ganglion, pacemaker potentials for the spontaneous periodic burst discharge are recorded with intracellular electrodes. The electrical activity is composed of slow potentials and superimposed spikes, and is divided into four types, which are: (a) "mammalian heart" type, (b) "slow generator" type, (c) "slow grower" type, and (d) "slow deficient" type. Since axons which are far from the somata do not produce slow potentials, the soma and dendrites must be where the slow potentials are generated. Hyperpolarization impedes generation of the slow potential, showing that it is an electrically excitable response. Membrane impedance increases on depolarization. Brief hyperpolarizing current can abolish the plateau but brief tetanic inhibitory fiber stimulation is more effective for the abolition. A single stimulus to the axon evokes the slow potential when the stimulus is applied some time after a previous burst. Repetitive stimuli to the axon are more effective in eliciting the slow potential, but the depolarization is not maintained on continuous stimulation. Synchronization of the slow potential among neurons is achieved by: (a) the electrotonic connections, with periodic change in resistance of the soma membrane, (b) active spread of the slow potential, and (c) synchronization through spikes.     

Tissue distribution of messenger RNAs coding for opioid peptide precursors and related RNA

All of the endogenous opioid peptides thus far identified are derived from three types of precursors, i.e. the corticotropin/beta-lipotropin precursor, preproenkephalin A and preproenkephalin B. Poly(A)-containing RNA from various bovine and porcine tissues has been subjected to blot hybridization analysis with the use of cDNA probes specific for the three opioid peptide precursors. Analysis with a corticotropin/beta-lipotropin precursor cDNA probe has revealed, in addition to the pituitary mRNA, a smaller hybridizable RNA species present in bovine extrapituitary tissues, such as the adrenal medulla, thyroid, thymus, duodenum and lung. The hypothalamus contains both these RNA species. DNA complementary to the smaller RNA species from the bovine adrenal medulla has been cloned. Analysis of the cloned cDNA, in conjunction with endonuclease S1 mapping of poly(A)-rich RNA from the adrenal medulla, has indicated that the smaller RNA species represents the 3'-terminal 712-729 nucleotides, excluding the poly(A) tail, of the pituitary corticotropin/beta-lipotropin precursor mRNA, having heterogeneous start sites. Analysis with a preproenkephalin A cDNA probe has shown the presence of hybridizable RNA in the bovine hypothalamus, duodenum and pituitary neurointermediate lobe in addition to the adrenal medulla. The hybridizable RNA species from all these tissues are indistinguishable in size. RNA hybridizable with a preproenkephalin B cDNA probe has been found in the porcine spinal cord and ileum besides the hypothalamus, and these RNA species exhibit an indistinguishable size. The results presented indicate that each opioid peptide precursor is synthesized in different tissues.     

A ring of uncharged polar amino acids as a component of channel constriction in the nicotinic acetylcholine receptor.

The channel pore of the nicotinic acetylcholine receptor (AChR) has been investigated by analysing single-channel conductances of systematically mutated Torpedo receptors expressed in Xenopus oocytes. The mutations mainly alter the size and polarity of uncharged polar amino acid residues of the acetylcholine receptor subunits positioned between the cytoplasmic ring and the extracellular ring. From the results obtained, we conclude that a ring of uncharged polar residues comprising threonine 244 of the alpha-subunit (alpha T244), beta S250, gamma T253 and delta S258 (referred to as the central ring) and the anionic intermediate ring, which are adjacent to each other in the assumed alpha-helical configuration of the M2-containing transmembrane segment, together form a narrow channel constriction of short length, located close to the cytoplasmic side of the membrane. Our results also suggest that individual subunits, particularly the gamma-subunit, are asymmetrically positioned at the channel constriction.     

Biosynthesis of Leaf Alcohol Formation of 3Z-Hexenal from Linolenic Acid in Chloroplasts of Thea sinensis Leaves

The synthetic activity for 3Z-hexenal, an important precursor of 3Z-hexenol (leaf alcohol), was localized in chloroplasts of Thea sinensis leaves. 3Z-Hexenal, which is easily isomerized to 2E-hexenal (leaf aldehyde), was formed from linolenic acid in the presence of oxygen. 13-l-Hydroperoxy-linolenic acid also served as a precursor, but the triglyceride and methyl ester of linolenic acid did not. This enzyme system appeared to be tightly bound to the lamellae membranes of chloroplasts.     

Water and carbon storage capacity in Isolatocereus dumortieri (Cactaceae) in an intertropical semiarid zone in Mexico

In the biosphere reserve Barranca de Metztitlán in Mexico, there is an extensive area with a semiarid scrub. The dominant species is the cactus Isolatocereus dumortieri. This is a key species in the ecosystem, because many species of birds, bats and insects are feeding from its nectar, pollen and fruits during the dry season thanks to their capacity to store water and carbon. However, there is no information about their potential to store water and carbon. The purpose of this study was to estimate the ability of I. dumortieri to store water and carbon. Water content per plant was estimated as 537.64 ± 71.59 L during the dry season and 692.24 ± 92.18 L during the wet season. In the same way the carbon stored per cactus was 16.75 kg ± 7.07 corresponding to 1.25 kg C m². The results shows the importance of I. dumortieri in maintaining the ecosystem services of the scrub vegetation.     

Effect of Ginkgo biloba extract on oxidative metabolism of valproic acid in hepatic microsomes from donors with the CYP2C9*1/*1 genotype

We investigated the effect of Ginkgo biloba extracts and some of its individual constituents on the oxidative metabolism of valproic acid (VPA) in hepatic microsomes from donors with the CYP2C9*1/*1 genotype. G. biloba extract decreased 4-ene-VPA, 3-OH-VPA, 4-OH-VPA, and 5-OH-VPA formation with mean (+/- SE) IC50 values of 340 +/- 40 microg/mL, 370 +/- 100 microg/mL, 180 +/- 30 microg/mL, and 210 +/- 20 microg/mL, respectively. This was associated with inhibition of not only CYP2C9*1, but also CYP2A6 and CYP2B6. Bilobalide, ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, quercetin-3-O-rutinoside, kaempferol-3-O-rutinoside, and isorhamnetin-3-O-rutinoside were not responsible for the inhibition of VPA metabolism by the extract. When analyzed as the sum of the aglycone and total glycosides present in the extract, quercetin decreased 4-ene-VPA, 4-OH-VPA, and 5-OH-VPA formation by 76%, 51%, and 70%, respectively, kaempferol decreased 4-ene-VPA, 4-OH-VPA, and 5-OH-VPA formation by 65%, 46%, and 49%, respectively, and isorhamnetin decreased 4-ene-VPA, 4-OH-VPA, and 5-OH-VPA formation by 29%, 26%, and 31%, respectively. The 3 aglycones did not affect 3-OH-VPA formation. In summary, G. biloba extract decreased hepatic microsomal formation of 4-ene-VPA, 4-OH-VPA, 5-OH-VPA, and 3-OH-VPA, but the effect was not due to the terpene trilactones or flavonol glycosides investigated in our study.     

Delimitation of the chromosomal region for a quantitative trait locus, qUVR-10, conferring resistance to ultraviolet-B radiation in rice (Oryza sativa L.)

Wide variation in ultraviolet-B (UVB) resistance is observed among rice varieties. In a previous study, three quantitative trait loci (QTLs) controlling UVB resistance were detected by QTL analysis, using backcross inbred lines (BILs) derived from a cross between a japonica cultivar, Nipponbare, and an indica cultivar, Kasalath. Among them, qUVR-10, a QTL for UVB resistance on chromosome 10, showed the largest effect. Plants homozygous for the Nipponbare allele at qUVR-10 were resistant to UVB, unlike those homozygous for the Kasalath allele. To determine more precisely the chromosomal location of qUVR-10, we performed a linkage mapping of qUVR-10 as a single Mendelian factor using advanced backcross progeny. Advanced progeny testing of F₄ families enabled us to determine the genotype classes of the qUVR-10 locus with high reliability. As a result, qUVR-10 was mapped between RFLP markers C60755S and C1757S, and co-segregated with C913A. In addition, a sequence showing high similarity to the Arabidopsis cyclobutane pyrimidine dimer (CPD) photolyase gene, which has been found to be involved in sensitivity to UV radiation in Arabidopsis and rice, was mapped in the candidate genomic region of qUVR-10. This result suggests that the CPD photolyase gene is a positional candidate for qUVR-10.Communicated by D.J. Mackill