603rd MEETING, LIVERPOOL
387
structure, obtained by oligosaccharide isolation and methylation
analysis, agrees with that first proposed by Katzenellenbogen &
Romanowska (1980) on the basis of methylation analysis alone.
structure Of serotype
lip0It also confirms that the
polysaccharide differs from that shared by the other Sh.flexneri
serotypes (Simmons, 197 1).
I thank Professor Bengt Lindberg (Department of Organic Chemistry, University of Stockholm)for carrying out the methylation analysis.
Katzenellenbogen, E. & Romanowska, E. (1980)Eur. J. Biochem. 113,
205-21 1
Simmons, D. A. R. (1971)Bacteriol. Rev. 35,1 1 7-148
Neuromuscular effects of intravenous anaesthetics (althesin and etomidate)
F. A. WALI
Anaesthetics Unit, The London Hospital, Whitechapel,
London E l , U.K.
The effects of the intravenous (i.v.) anaesthetic agents althesin
and etomidate on the contractile responses produced by
repetitive nerve stimulation, acetylcholine (ACh) and tetraethylammonium (TEA) were studied in the isolated chick
biventer cervicis (BVC) nerve-muscle preparation.
Repetitive nerve stimulation at 0.2 Hz with 5 V and 0.5 ms
pulse duration, produced twitch contractions in the chick BVC
muscle. Althesin ( 6 6 ~ and
~ ) etomidate (120,UM) produced an
increase in the amplitudes of the twitch contractions by about
3 2 k 1.1% and 28 fO.8% (n = 6) respectively.
ACh (0.55-1 1mM) and TEA (2.4-12m~) produced concentration-dependent contractures in the chick muscle. A
maximum response of 4.7fO.l g tension for ACh and
1.9 f0.09 g tension for TEA was obtained with 5.5 mM-ACh and
~ . ~ ~ M - T E( nA=,6) respectively. Althesin and etomidate
reduced the ACh-induced contractures, whereas they increased
the contractures produced by TEA. The results are shown in
Table 1.
The actions of althesin and etomidate were reversible upon
washing out the drugs for about 10-15 min. The present results
show that the i.v. anaesthetics althesin and etomidate produce
similar neuromuscular effects to that produced by rnethohexitone in the chick BVC muscle (Bell & Wali, 1981: Elliott &
Wali, 1983). It is possible that the i.v. anaesthetics produce both
pre- and post-synaptic actions at the neuromuscular junction.
More experiments, using intracellular recording technique and
radioactive agents, are needed to further investigate these
actions at the vertebrate neuromuscular junction.
Bell, C. & Wali, F. A. (1981)Br. J. Pharmacol. 73,31 1P
Elliott, R. C. & Wali, F. A. (1983)Neuropharrnacology, 22, 151-155
Table 1. Effect of althesin and etomidate on the ACh- and TEA-induced contractures in the chick BVC muscle (n = 6)
Results are means f S.E.M. Abbreviation used: ED,,, estimated dose of a drug which if injected will produce a 50% of the maximum
response in the tissue.
ED,, (mM)
\
ACh contractures
TEA contractures
A
I
Control
Anaesthetic
(C)
Althesin ( 6 6 ~ ~ ) 0.64k0.2
Etomidate ( 1 2 0 ~ ~ )0.54+0.1
\
Test
(TI
1.9k0.6
Ratio
1.5+0.1
2.8
TIC
3.0
A
r
Control
(C)
8.4k0.1
6.6k0.1
Test
(T)
1.9k0.1
3.0T0.1
\
Ratio
TIC
0.2
0.5
The influence of plant growth temperature on the lipid/protein ratio of chloroplast thylakoid
membranes
DAVID J. CHAPMAN, PAUL A. MILLNER and
JAMES BARBER
ARC Photosynthesis Research Group, Department of Pure and
Applied Biology, Imperial College of Science and Technology,
London S W 7 2BB, U.K.
Alteration of membrane fluidity by changes in lipid composition
is a central feature of the adaptation of membranes to different
temperatures. This could be of particular significance in the case
of the thylakoid membrane of higher plants, because the
photosynthetic electron-transport reactions are almost certainly
dependent on the lateral mobility of various components,
including the hydrophobic redox carrier plastoquinone. An
adaptive change in the membrane fluidity resulting from an
increase in unsaturation of fatty acids at low temperatures
occurs in many membrane systems, including some membranes
of higher plants. However, in thylakoids from Pisum safiuum
(pea) plants we found no substantial effect of low growth
temperature (6OC) on fatty acid composition (Chapman et al.,
VOl. 11
1983). Using essentially the same methods as described in this
previous investigation, we analysed the fatty acid composition of
thylakoids isolated from four other plant species (Table I). In
the two species known to be resistant to chilling (less than 10°C)
temperatures, Lolium temulentum (darnel) and winter oats
(Auena satiua, cv. Pennal), there were no significant differences in overall fatty acid unsaturation between plants grown
at 6OC and 18OC. As well as the lack of a phenotypic response
in fatty acid composition to growth temperature there was also
an absence of a genotypic adaptation. This is seen in the
similarity of unsaturation in the chilling-resistant species and the
species genetically suited to higher temperature conditions
[cucumber (Cucumis sativus) and marrow (Cucurbita pepo),
chilling-sensitive I.
Although the fatty acid unsaturation of thylakoid lipids does
not seem to be related to adaptation to low growth temperatures, we have found that the amount of lipid in the
membrane does seem to be involved. Table 1 shows that, for a
single species, growth at low temperature results in higher