The effect of displacement current on the measurement of reversal potential in squid giant axon

The measurement of the sodium reversal potential (Erev), as that potential where the early current reverses during voltage clamp, was found to exceed the true Erev by 4.1 +/- 2.4 mV (mean +/- SD) in squid giant axon. This error was found in both intact and internally perfused axons and is due to interference from the displacement current. This was shown by subtraction of the current records obtained before and after treatment with tetrodotoxin (TTX). The error in Erev is proportional to (Td/gNA)12 where Td is the time constant of the displacement current.     

Nutrition and muscle potassium: differential effect in rat slow and fast muscles

The effects of malnutrition on intracellular K+ activity, (alpha K)i, and membrane potential, Em, were measured by means of double-barrelled K+-selective microlectrodes in the soleus and gastrocnemius muscles of the rat. (alpha K)i and Em were measured in vivo in normal anaesthetized animals and in rats subjected to one of two diet restrictions: a 2-day fast or a long-term hypocaloric diet. In the soleus muscle, (alpha K)i fell by similar amounts in both 2-day fasted and long-term hypocalorically fed rats, while Em depolarized significantly only in hypocalorically fed rats. In the gastrocnemius muscle, neither the 2-day fast nor the hypocaloric diet affected (alpha K)i or Em. It is suggested that the selective loss of K+ from the soleus muscle may be related to its activity pattern.     

Characterization of the sulfonylurea receptor on beta cell membranes

Specific, high affinity sulfonylurea receptors were characterized on membranes of an insulin-secreting hamster beta cell line (HIT cells). Saturable binding of the sulfonylurea, [3H]glyburide, was linear up to 0.8 mg/ml membrane protein. Scatchard analysis of equilibrium binding data at room temperature indicated the presence of a single class of saturable, high affinity binding sites with a Kd of 0.76 +/- 0.04 nM and a Bmax of 1.09 +/- 0.13 pmol/mg protein, n = 9. The insulin secretory potency of glyburide, glipizide, tolbutamide, tolazamide, and carboxytolbutamide was compared to the ability of these ligands to displace [3H]glyburide from the sulfonylurea receptor. Tolbutamide, tolazamide, and glipizide demonstrated reasonable agreement with ED50 values of 15 microM, 3 microM, and 30 nM and Ki values of 25.3 microM, 7.2 microM, and 45 nM, respectively. The inactive tolbutamide metabolite, carboxytolbutamide, at the highest concentration tested, only partially displaced [3H]glyburide from the receptor and was a very poor secretagogue. At 37 degrees C the affinity of [3H]glyburide binding, Kd = 2.0 nM, was similar to the ED50 of 5.5 nM when the free glyburide concentrations were corrected for binding of the drug to albumin. These studies suggest that sulfonylureas initiate their biologic effect through a high affinity, specific interaction with sulfonylurea receptors on the beta cell membrane.     

Linkage studies of Usher syndrome type 1: exclusion results from the Usher syndrome consortium.

Usher Syndrome Type 1 is an autosomal recessive disease characterized by profound congenital hearing impairement and vestibular dysfunction followed by the onset of retinitis pigmentosa in childhood or early adolescence. Members of the Usher Syndrome Consortium, whose objective is to locate and isolate the genes for Usher syndrome, have pooled linkage data from 36 families with 111 affected individuals. We report the analysis of 206 blood group, protein, and DNA marker polymorphisms. No evidence of linkage heterogeneity among families was found for any of the markers studied; the negative lod scores exclude the locus for this disease from about 39% of the genome. Our results indicate the regions of the genome to which our continuing efforts should be directed.     

Comparative action of glyphosate as a trigger of energy drain in eubacteria.

Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa, each possessing a 5-enolpyruvylshikimate 3-phosphate synthase that is sensitive to inhibition by glyphosate [N-(phosphonomethyl)glycine], provide a good cross-section of organisms exemplifying the biochemical diversity of the aromatic pathway targeted by this potent antimicrobial compound. The pattern of growth inhibition, the alteration in levels of aromatic-pathway enzymes, and the accumulation of early-pathway metabolites after the addition of glyphosate were distinctive for each organism. Substantial intracellular shikimate-3-phosphate accumulated in response to glyphosate treatment in all three organisms. Both E. coli and P. aeruginosa, but not B. subtilis, accumulated near-millimolar levels of shikimate-3-phosphate in the culture medium. Intracellular backup of common-pathway precursors of shikimate-3-phosphate was substantial in B. subtilis, moderate in P. aeruginosa, and not detectable in E. coli. The full complement of aromatic amino acids prevented growth inhibition and metabolite accumulation in E. coli and P. aeruginosa where amino acid end products directly control early-pathway enzyme activity. In contrast, the initial prevention of growth inhibition in the presence of aromatic amino acids in B. subtilis was succeeded by progressively greater growth inhibition that correlated with rapid metabolite accumulation. In B. subtilis glyphosate can decrease prephenate concentrations sufficiently to uncouple the sequentially acting loops of feedback inhibition that ordinarily link end product excess to feedback inhibition of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase by prephenate. The consequential unrestrained entry is an energy-rich substrates into the aromatic pathway, even in the presence of aromatic amino acid end products, is an energy drain that potentially accounts for the inability of end products to fully reverse glyphosate inhibition in B. subtilis. Even in E. coli after glyphosate inhibition and metabolite accumulation were allowed to become fully established, a transient period where end products were capable of only partial reversal of growth inhibition occurred. The distinctive metabolism produced by dissimilation of different carbon sources also profound effects upon glyphosate sensitivity.     

Spatial variation in larval concentrations as a cause of spatial variation in settlement for the barnacle,Balanus glandula

Summary Settlement rates of the high intertidal barnacle, Balanus glandula, were monitored at three sites in the rocky intertidal zone in Central California simultaneously with measurements of larval concentrations in the adjacent water column. In both 1983 and 1984, settlement rates onto vacant substrate differed among the sites by nearly two orders of magnitude. For all sampling dates, this spatial variation in settlement mirrored the spatial distribution of Balanus glandula cyprid concentration in the water column. A perfect rank correlation was found between cyprid concentrations near a site and subsequent settlement. A noteworthy observation was that the sites switched rank in their settlement rates from 1983 to 1984. This change in settlement rankings matched a switch in rankings for cyprid concentrations.Settlement itself appears to be an important cause of the spatial pattern of cyprid concentrations. Comparing the rates of settlement to estimates of the number of cyprids available at a site suggests that settlement causes a large drain on the cyprid population as a water mass passes over successive sites. No consistent spatial patterns were found in the distribution of other major plankton groups (calanoid copepods) that are similar in size to Balanus cyprids but do not settle.The large differences in settlement rates among these sites were previously shown to be a leading cause of large differences in the structure of benthic barnacle populations. The close correspondence shown here between these large differences in settlement and differences in larval concentrations suggests that nearshore oceanic processes affecting larval arrival contribute to the control of benthic community structure.     

Nitrogen inputs to a marine embayment: the importance of groundwater

We examined the importance of nitrogen inputs from groundwater and runoff in a small coastal marine cove on Cape Cod, MA, USA. We evaluated groundwater inputs by three different methods: a water budget, assuming discharge equals recharge; direct measurements of discharge using bell jars; and a budget of water and salt at the mouth of the Cove over several tidal cycles. The lowest estimates were obtained by using a water budget and the highest estimates were obtained using a budget of water and salt at the Cove mouth. Overall there was more than a five fold difference in the freshwater inputs calculated by using these methods. Nitrogen in groundwater appears to be largely derived from on site septic systems. Average nitrate concentrations were highest in the region where building density was greatest. Nitrate in groundwater appeared to behave conservatively in sandy sediments where groundwater flow rates were high (> 11/m²/h), indicating that denitrification was not substantially reducing external nitrogen loading to the Cove. Nitrogen inputs from groundwater were approximately 300 mmol-N/m³/y of Cove water. Road runoff contributed an additional 60 mmol/m³/y. Total nitrogen inputs from groundwater and road runoff to this cove were similar in magnitude to river dominated estuaries in urbanized areas in the United States.     

Magnification in Drosophila: evidence for an inducible rDNA-specific recombination system

An experiment is described that provides evidence for an exchange mechanism to explain the increase in ribosomal gene number that occurs during bobbed magnification. We show that bobbed and bobbed-lethal alleles do not magnify in closed X chromosomes, but that a spontaneous ring opening restores normal magnification. The results provide strong evidence that the elementary magnifying event is unequal sister chromatid exchange, and can be interpreted in the framework of an inducible rDNA-specific recombination system as the basis of ribosomal gene magnification. Correspondence to: S.A. Endow at the above address     

Neisseria gonorrhoeae possesses two nicotinamide adenine dinucleotide-independent lactate dehydrogenases

Abstract An important metabolic capability of Neisseria gonorrhoeae is the utilization of host-derived lactate. Two isoenzymes of the membrane-associated, pyridine dinucleotide-independent type of lactate dehydrogenase (iLDH) participate in lactate assimilation, but exhibit distinctive properties. Isoenzyme iLDH-I utilized lactate exclusively as substrate, exhibiting a preference for the D-isomer. In contrast, isoenzyme iLDH-II exhibited broad substrate specificity (lactate, phenyllactate, and 4-hydroxyphenyllactate), but was stereospecific for the L-isomers. These results explain the difficulty in isolating mutants unable to utilize lactate.