The effect of tetrodotoxin on the sodium gating current in the squid giant axon.

The effect of tetrodotoxin (TTX) on the sodium gating current in the squid giant axon was examined by recording the current that flowed at the pulse potential at which the ionic current fell to zero, first in the absence and then in the presence of TTX. The addition of 1 microM TTX to the bathing solution had no consistent effect on the size of the initial peak of the gating current, but resulted in small changes in the timecourse of its subsequent relaxation which were mainly caused by a reduction of about one quarter in the component that has a delayed onset and may possibly arise from changes in the state of ionization of groups in the channel wall when the lumen fills with water. Our findings suggest that the binding of TTX at the outer face of the sodium channel does not interfere with the mechanisms of activation and inactivation by the voltage sensors, but has an allosteric effect on the access of internal cations to the inside of the channel.     

Hydroxyl ion movements across the human erythrocyte membrane. Measurement of rapid pH changes in red cell suspensions

A stopped flow rapid reaction apparatus capable of following changes of ±0.02 pH unit in 0.1 ml of solution in less than 0.005 sec has been developed, utilizing a commercially available pH-sensitive glass electrode. Using this instrument, extracellular pH at 37°C was followed from less than 0.025 sec to 300 sec after mixing equal volumes of the following CO₂-free solutions: (A) normal human red cells, washed three times and resuspended in 150 mM NaCl at pH 7.2 with a hematocrit of 18%; and, (B) 150 mM NaCl adjusted with HCl or NaOH to pH 2.1 to pH 10.3. A minimum of 2 ml of mixture had to flow through the electrode chamber to ensure complete washout. The mixing process produced a step change in the pH of the extracellular fluid, after which exchanges across the red cell membrane and buffering by intracellular hemoglobin caused it to return toward pH 7.2 with an approximately exponential time course. Under the assumption that pH changes after mixing represent exchanges of hydroxyl for chloride ions across the cell membrane, hydroxyl ion permeabilities (P _OH ^- in cm/sec) were calculated and found to vary from 2 x 10^-4 at pH 9 to 4 x 10^-1 at pH 4 according to the empirical relationship P _OH ^- = 170 exp (-1.51 pH). The form of the dependence of P _OH ^- on extracellular pH does not appear compatible with a simple fixed charge theory of membrane permselectivity.     

ISL2, a new mobile genetic element in Lactobacillus helveticus

Spontaneous, phenotypically stable mutations at the -galactosidase locus (lacL-lacM) in Lactobacillus helveticus were identified and analyzed. We found that a significant number of mutations were caused by integration of a new IS element, ISL2, into these lac genes. ISL2 is 858 by long, flanked by 16-bp perfect inverted repeats and generates 3-bp target duplications upon insertion. It contains one open reading frame, which shows significant homology (40.1 % identity) to the putative transposase of IS702 from Cyanobacterium calothrix. ISL2 is present in 4–21 copies in the L. helveticus genome, but it is not found in other lactic acid bacteria. Its divergence in copy number and genomic locations in different L. helveticus strains makes it useful as a tool for strain identification by genetic fingerprinting.     

Letter from the Editors

Transgenic Research -     

Polyhydroxyphenyläther aus der phaeophycee Sargassum muticum

From an acetylated fraction of Sargassum muticum (Yendo) Fensholt were isolated: phloroglucinol tri-acetate; diphlorethol pentaacetate (2,4,6,3′,5′-pentaacetoxydiphenyl ether), bifuhalol hexaacetate (2,4,6,3′,4′,5′-hexaacetoxydiphenyl ether), trifuhalol A octaacetate (2,6-diacetoxy-1-(3,4,5-triacetoxyphenoxy)-4-(2,4,6-triacetoxy- phenoxy)-benzene), and the new trifuhalol B octaacetate(3,5-diacetoxy -1-(2,4,6-triacetoxyphenoxy)-2-(3,4,5- triacetoxyphenoxy)-benzene).