Membrane resistance change of the frog taste cells in response to water and Nacl

The electrical properties of the frog taste cells during gustatory stimulations with distilled water and varying concentrations of NaCl were studied with intracellular microelectrodes. Under the Ringer adaptation of the tongue, two types of taste cells were distinguished by the gustatory stimuli. One type, termed NaCl-sensitive (NS) cells, responded to water with hyperpolarizations and responded to concentrated NaCl with depolarizations. In contrast, the other type of cells, termed water-sensitive (WS) cells, responded to water depolarizations and responded to concentrated NaCl with hyperpolarizations. The membrane resistance of both taste cell types increased during the hyperpolarizing receptor potentials and decreased during the depolarizing receptor potentials, Reversal potentials for the depolarizing and hyperpolarizing responses in each cell type were a few millivolts positive above the zero membrane potential. When the tongue was adapted with Na-free Ringer solution for 30 min, the amplitude of the depolarizing responses in the NS cells reduced to 50% of the control value under normal Ringer adaptation. On the basis of the present results, it is concluded (a) that the depolarizing responses of the NS and WS cells under the Ringer adaptation are produced by the permeability increase in some ions, mainly Na+ ions across the taste cell membranes, and (b) that the hyperpolarizing responses of both types of taste cells are produced by a decrease in the cell membrane permeability to some ions, probably Na+ ions, which is slightly enhanced during the Ringer adaptation.     

In VivoP NMR Studies of Corn Root Tissue and Its Uptake of Toxic Metals

Excised corn root tissue has been evaluated for its viability, integrity of compartmentation, intracellular pH gradients, total mobile phosphorus content and nucleotide concentrations under different levels of acidity, and mineral stresses using in vivo³¹P nuclear magnetic resonance spectroscopy at 21 to 23°C. Perfusion with Al³⁺ ion at low pH (4.0) for 20 hours caused the overall concentration of nucleotides in the cytoplasm to decrease significantly relative to the control. Respiratory activity as measured by O₂ uptake decreased by a comparable amount over this time period. The addition of glucose to the Al-containing perfusate negated the inhibitory effects on the respiratory system. Treatment of the tissue with paramagnetic manganese ion while perfusing in the presence of O₂ allowed for the observation of the sequence of events leading to the irreversible trapping of Mn²⁺ in the vacuole. Pretreatment of the roots with Mg²⁺ prevented Mn²⁺ migration to the vacuole over the time period of this experiment. Hypoxia prevented all but a limited uptake of Mn²⁺ into the cytoplasm of the root tips. No evidence of Mn²⁺ complexation of either cytoplasmic or vacuole Pi suggests that the energy derived from O₂ consuming processes is necessary for the facilitated movement of this divalent cation.     

Effect of indomethacin on bombesin-like immunoreactivity, somatostatin and gastrin secretion from rat stomach

In the present study the effect of indomethacin-induced prostaglandin deficiency was examined on the release of bombesin-like immunoreactivity (BLI), a putative peptidergic neurotransmitter, from the isolated perfused rat stomach. In addition, gastrin and somatostatin (SLI) secretion was determined. Pretreatment of rats with indomethacin (2 mg/kg X h) resulted in a 3-fold increase of basal BLI secretion. In response to acetylcholine (2 X 10(-6) M) BLI rose from 2,000 to 4,000 pg/min, whereas in controls BLI increased from 400 to 1,400 pg/min. While absolute values for BLI secretion were higher in indomethacin-treated stomachs the relative increase above baseline was lower (100 vs. 250%). In control rats the increase in BLI secretion in response to acetylcholine was abolished when the acidity in the gastric lumen was increased from pH 7 to pH 2. After indomethacin, however, the stimulatory effect of acetylcholine during luminal pH 7 and pH 2 was identical. The decrease of SLI by acetylcholine at luminal pH 7 was abolished in indomethacin-treated stomachs in response to 10(-6) M acetylcholine, and 2 X 10(-6) M had even a stimulatory effect on SLI secretion. Indomethacin pretreatment reduced gastrin secretion at luminal pH 7. These data demonstrate that endogenous prostaglandins exert an inhibitory tone on basal and stimulated BLI and stimulated SLI secretion in the rat stomach. It is suggested that endogenous prostaglandins also inhibit the release of a peptidergic neurotransmitter, similar to their effect on the classical neurotransmitters acetylcholine and norepinephrine.     

Molecular evidence for the rapid propagation of mouse t haplotypes from a single, recent, ancestral chromosome

Mouse t haplotypes are variant forms of chromosome 17 that exist at high frequencies in worldwide populations of two species of commensal mice. To determine both the relationship of t haplotypes to each other and the species within which they exist, 35 representative t haplotypes were analyzed by means of 10 independent molecular probes, including five DNA clones and five polypeptide spots identified by means of two- dimensional gel electrophoresis. All of the tested haplotypes were found to share restriction fragments and polypeptide spots that are absent in mice carrying wild-type forms of chromosome 17. This observation provides the first direct evidence that all of the known t haplotypes are descendents of a single ancestral chromosome. The absence of variation among t haplotypes could mean that this ancestral chromosome existed relatively recently, in which case it would be necessary to postulate introgressions of t haplotypes across species lines to explain their presence in both Mus domesticus and M. musculus. Alternatively, it is possible that the ancestral chromosome existed prior to the split between M. domesticus and M. musculus and that, by chance, our probes fail to detect polymorphisms that exist among the t haplotypes. A further result of our analysis is the characterization of a partial t haplotype in a wild population of Israeli mice.      

Nucleosomal structure as probed by H3 histone thiol reactivity

Two H3 histone variants are found in equal amount in HeLa cells, and they have been characterized by two-dimensional gel electrophoresis followed by reaction with specific antibodies. These molecules are the only cysteine-containing histones, and they have been used as the target for thiol-specific reagents, in intact nuclei, isolated nucleosomes, histone complexes, and purified histones. Cysteine residues are available toN-ethylmaleimide only when histones are disassembled from the core particles. Upon reaction with these reagents, one of the H3 variants undergoes profound conformational changes, as revealed by an altered electrophoretic mobility.     

A budding and fusing journey through the secretory pathway. Genetic and In Vitro Analysis of Cell Compartmentalization: A UCLA symposium, Taos, NM, USA, February 3-9, 1990

Reconstitution of vesicular transport events and the molecular and genetic analysis of the secretory pathway have taken the field of membrane traffic into a new era. Already, proteins have been discovered that facilitate multiple transport steps, and studies of the identities and modes of action of additional transport components, such as those that specify the targets of transport vesicles, will soon follow. Even after we understand how transport vesicles form, find their targets, and then fuse, other fundamental questions will still remain. How are proteins sorted into distinct transport vesicles? How is the directionality of protein transport achieved? How do organelles maintain their identities in the face of large volumes of membrane traffic? Finally, how is membrane traffic regulated? Answers to each of these fundamental questions are likely to be available in the not-too-distant future.     

Antiangiogenic activity of chemopreventive drugs

Tumors growing within the host form dynamic aberrant tissue that consists of host components, including the stroma, an expanding vasculature and often chronic inflammation, in addition to the tumor cells themselves. These host components can contribute to, rather than limit, tumor expansion, whereas deprivation of vessel formation has the potential to confine tumors in small, clinically silent foci. Therapeutic inhibition of vessel formation could be best suited to preventive strategies aimed at the suppression of angiogenesis in primary tumors in subjects at risk, or of micrometastases after surgical removal of a primary tumor. Our analysis of potential cancer chemopreventive molecules including N-acetylcysteine, green tea flavonoids and 4-hydroxyphenyl-retinamide has identified antiangiogenic activities that could account--at least in part--for the tumor prevention effects observed with these compounds. These drugs appear to target common mechanisms of tumor angiogenesis that may permit identification of critical targets for antiangiogenic therapy and antiangiogenic chemoprevention.