Eight patients with a short bowel resulting from intestinal resection and clinically stable for at least 6 mo were studied on two diets. Each diet was given for 5 days at a time and crossed over with the other. Both diets contained 20% of total calories as protein. The high-fat diet had 60% of calories as fat and 20% as carbohydrate. This ratio was reversed in the high-carbohydrate diet. Both diets were lactose free with low fiber. Fluid intake was kept constant. The results showed that there was no difference in the blood chemistry, stool, or ostomy volume, the zinc, calcium, and magnesium balances, urine volume, and electrolyte excretion between patients on the two diets. Bomb calorimetry showed that the total calories absorbed and excreted were comparable between the two diets. It was concluded that low-fat diets had no special benefit in the overall nutrition of the patient who has been in remission in regard to bowel disease for 6 mo or longer. Hence, dietary restriction is not recommended in these patients. However, this study did not resolve the question of the requirements and losses of fat-soluble vitamins in such patients when on a high-fat diet.

Adult↗

PubMed1982

Open-state substructure of single chloride channels from Torpedo electroplax.

Chloride channels from Torpedo californica electroplax were inserted into planar phospholipid membranes, and single-channel currents were studied at high time-resolution. The open channel fluctuates rapidly between three substates, with conductances of 18.5, 9.4 and 0 pS in 150 mM Cl-. Under various ionic conditions the three substates are always equally spaced in conductance; at various voltages leading to different probabilities of observing the three substates, the substate frequencies are always binomially distributed. The conclusion emerges that the conducting of unit of Cl- channel is composed of two identical Cl- diffusion pathways, each with a voltage-dependent gate.

Animals↗

PubMed1982

The pottery and plumbism puzzle.

Explore the source record for details and available documents.

Adult↗

PubMed1982

Australia leads world in switch to no-lead cans. Worry over baby foods.

Explore the source record for details and available documents.

Australia↗

PubMed1982

Specific calcium antagonist binding sites in brain.

The binding of the calcium antagonist [3H] nitrendipine ([3H] NDP) to brain and heart is described and the brain site is characterized. The binding is saturable, specific and of very high affinity with KD values of 0.16 nM in brain and 0.21 nM in heart. Our kinetic results are similar to those recently reported by two other groups (1, 2), indicating a saturable, high affinity binding site in brain. In brain the binding sites are enriched in crude nuclear and synaptosomal fractions. The highest levels of binding are seen in the hippocampus, caudate and cerebral cortex with much lower levels in the cerebellum and pons. Calcium has a marked stimulatory effect on [3H] NDP binding at 10(-4) M. Addition of 0.5 mM CaCl2 to EDTA treated membranes nearly doubles the number of binding sites. Of the many drugs and neurotransmitters tested only other calcium antagonists, i.e. verapamil, inhibit binding (IC50 = 250 nM). The inhibition of [3H] NDP binding by verapamil is apparently non-competitive and not complete, suggesting that [3H] NDP binds to several sites, only some of which are inhibited by verapamil. The [3H] NDP binding site is probably a protein since it is very sensitive to trypsin, heat and sulfhydryl reagents.

Animals↗

PubMed1982

Studies on the involvement of the UGA readthrough process in the mechanism of attenuation of the tryptophan operon of Escherichia coli.

We asked if UGA suppression by charged tRNATrp, a process called UGA readthrough, is involved in the mechanism of attenuation of the tryptophan (trp) operon in Escherichia coli. For this purpose we used two mutations: strA(LD1) which causes restriction of UGA readthrough, and revA which partially overcomes the restriction of UGA readthrough caused by strA(LD1)(Engelberg-Kulka et al. 1982). trp attenuation was monitored by the regulation of the synthesis of the trp operon enzyme anthranilate synthetase (ASase) in trpR strains. We showed that the strA(LD1) mutation causes a significant increase in the level of synthesis of ASase in the presence of an excess of tryptophan, while the revA mutation reverses this effect, indicating that transcription termination at the trp attenuator site is relieved by restriction of UGA readthrough. Based on our results and the sequence data of the trp leader RNA of E. coli (Oxender et al. 1979), we offer a model for the involvement of the UGA readthrough process in trp attenuation. We suggest that the UGA readthrough process permits trp attenuation to respond to slight changes in the cellular concentration of charged tRNATrp.

Anthranilate Synthase↗

PubMed1982

Coupling of water and ion fluxes in a K+-selective channel of sarcoplasmic reticulum.

Streaming potentials arising across a K+-selective channel from fragmented sarcoplasmic reticulum were measured by incorporating the channel into planar bilayer membranes and imposing osmotic gradients across the membranes by addition of sorbitol or urea to only one side. Single-channel zero-current potentials were determined, and dilution artifacts were corrected for by addition of valinomycin to the bilayer. The streaming potentials were found to be unusually small, 1.1 mV per osmolal. The potentials were linearly related to the osmotic gradient across the bilayer, and were identical for sorbitol and urea. The results imply that the channel cannot be envisioned as a long tube, like gramicidin, but rather as a short constriction of less than 10 A in length opening out into wider mouths on either side of the membrane.

Animals↗

PubMed1982

Isolated-patch recording from liposomes containing functionally reconstituted chloride channels from Torpedo electroplax.

Small unilamellar vesicles formed from purified phospholids by detergent/dialysis methods may be enlarged to 30-microns diameter by freezing and thawing. Very-high-resistance seals were formed by applying a glass micropipette to the surface of these large liposomes, and single bilayer "patches" of membrane were isolated from the liposome surface while remaining sealed to the micropipette. The exogenous channel-forming peptides gramicidin and alamethicin induced characteristic single-channel fluctuation behavior in these excised patches held under voltage-clamp conditions. Large liposomes were formed from the small unilamellar vesicles made from cholate extracts of Torpedo electroplax plasma membrane vesicles. Isolated patches formed from these reconstituted membranes displayed current fluctuations due to single voltage-gated Cl- channels from non-innervated-face membranes; the properties of these Cl- channels are identical to those observed in planar bilayer membranes after direct insertion from native membranes. This liposome-patch method combines the advantages of membrane protein incorporation into liposomes with high-resolution electrical recording methods and may provide a generally applicable approach to the study of integral membrane channel proteins after solubilization and reconstitution.

Animals↗

PubMed1982

Determination of critical anthropometric parameters for design of respirators.

The objectives of this study were 1) to collect useful anthropometric data from 243 workers fit-tested in a continuing respirator fit-test program; and 2) to determine correlation between anthropometric data and Protection Factor obtained from quantitative fit-testing for half-mask respirators. Anthropometric data were collected from two direct facial measurements [nasal root breadth (NRB), and face-length (FL)] and five indirect facial measurements [nose length, nose protrusion, chin length, mouth width (MW), and face width (FW)] from front- and side-view slides of test subjects. For quantitative analysis, the anthropometric data collected in this study were normalized with relevant respirator dimensions (for four different brands and ten sizes). Results of linear regression analysis indicated that correlation coefficients between Protection Factor and anthropometric data (FL, MW, FW and NRB) were respectively - 0.04, 0.22, 0.30 and 0.04. These correlation coefficients are for white males without facial hair. The "critical" anthropometric parameters as apparent from the analysis were MW and FW. However, a person with certain combination(s) of multiple anthropometric parameters may provide a better correlation with Protection Factor.

Anthropometry↗

PubMed1982

Conduction and block by organic cations in a K+-selective channel from sarcoplasmic reticulum incorporated into planar phospholipid bilayers.

A collection of organic cations has been used to probe the gross structural features of the ionic diffusion pathway in a K+-selective channel from sarcoplasmic reticulum (SR). Channels were incorporated into planar phospholipid bilayer membranes, and single-channel currents were measured in the presence of ammonium-derived cations in the aqueous phases. Small monovalent organic cations are able to permeate the channel: the channel conductance drops sharply for cations having molecular cross sections larger than 18-20 A2. Impermeant or poorly permeant cations such as tetraethylammonium, choline, and glucosamine, among others, block K+ conduction through the channel. This block is voltage dependent and can be described by a one-site, one-ion blocking scheme. 19 monovalent organic cations blocks primarily from the trans side of the membrane (the side defined as zero voltage), and much more weakly, if at all, from the cis side (to which SR vesicles are added). These blockers all appear to interact with a site located at 63% (average value) of the electric potential drop measured from the trans side. Furthermore, block by 1,3-bis[tris(hydroxymethyl)-methylamino] propane (BTP) shows that the presence of a blocking ion increases the duration of the apparent open state, as expected for a scheme in which the blocking site can be reached only when the channel is open. The results lead to a picture of the channel containing a wide (at least 50 A2) nonselective trans entry in series with a narrow (20 A2) constriction.

Animals↗

PubMed1982

Bis-quaternary ammonium blockers as structural probes of the sarcoplasmic reticulum K+ channel.

A series of n-alkyl-bis-alpha,omega-trimethylammonium (bisQn) compounds was synthesized, and their ability to block K+ currents through a K+ channel from sarcoplasmic reticulum was studied. K+ channels were inserted into planar phospholipid membranes, and single-channel K+ currents were measured in the presence of the blocking cations. These bisQn compounds block K+ currents only from the side of the membrane opposite to the addition of SR vesicles (the trans side). The block is dependent on transmembrane voltage, and the effective valence of the block (a measure of this voltage dependence) varies with the methylene chain length. For short chains (bisQ2-bisQ5), the effective valence decreases with chain length from 1.1 to 0.65; it then remains constant at approximately 0.65 for bisQ5 to bisQ8; the effective valence abruptly increases to 1.2-1.3 for chains of nine carbons and longer. For the compounds of nine carbons and longer, the discrete nature of the block can be observed directly as 'flickering noise" on the open channel. The kinetics of the block were studied for these long-chain blockers. Both blocking and unblocking rates of the blockers vary with chain length, with the blocking rate showing the strongest variation--an increase of 2.8-fold per added methylene group. All of the voltage dependence of the binding equilibrium resides in the blocking rate, and none in the unblocking rate. The results imply that 65% of the voltage drop within the channel occurs over a distance of 6-7A, and that the short-chain blockers bind in a bent-over conformation with both charges deeply inside the channel.

Animals↗