Evolution of C6, C8 and C10 acids and their ethyl esters in cells and musts during fermentation with threeSaccharomyces cerevisiae races

Summary The evolution of the cell and must contents of three short-chain fatty acids (C₆, C₈ and C₁₀) and their ethyl esters during fermentations withSaccharomyces cerevisiae racescerevisiae, bayanus andcapensis were studied. The former is a fermentative yeast and the last two are flor film yeasts. The acid concentrations in the musts increased throughout the alcoholic fermentations, and maximum cell concentrations of the fatty acids were reached after 48 h of fermentation. Maximum ester concentrations in the cells were attained after 48–72 h of fermentation. In the musts, ethyl octanoate and ethyl decanoate reached a peak also at this point, and ethyl hexanoate after 10 days. After 134 days,S. cerevisiae racecapensis formed a thick flor film whileS. cerevisiae racebayanus developed a thin film andS. cerevisiae racecerevisiae formed no film. At this point, acid contents remained constant in the wines produced byS. cerevisiae racescerevisiae andbayanus, and decreased in those obtained with racecapensis. The ethyl ester contents tended to decrease with the exception of ethyl decanoate in the fermentations carried out byS. cerevisiae racescerevisiae andbayanus.     

Biological reasons for the unsuitability of growth parameters and indices for comparing fish growth

Parameters k and L in the Von Bertalanffy equation and their derivatives =kL, = logk + 2logL; as well as slopes b_L/t of the regression L=at^b (t, years), relative increments (CI=[L₂–L₁]/L₁), specific growth rates (C_v=InL₂–InL₁), growth characteristics (Clh = CvxL₁) and growth constants (Clt=Cvx[t₂ + t₁]/2) were analyzed. A total of 121 bream Abramis brama stocks in the first 10 years of life were studied. At the same real growth rate (the average absolute linear annual increments, mm year^–1) the values of k, L, , , b_L/t, CI, Cv and Clt in different stocks vary within almost the whole range. The main reason is the natural process of growth self-regulation: the relation between the average body lengths in the first year (L₁) and the relative growth rates (slopes b_L/t) is negative (b_L/t = exp[0.1183–0.0053L₁], r=0.76). The above relation defines 4 principal types of the Ford-Walford lines. Thirty four percent of the stocks have rather steep slopes of the lines and even parallel the absolute slope of 45°, so the L values of these stocks have no biological significance. The authors recommend a simple and more precise, from a biological point of view, approach for comparing fish population growth rates.     

Use-dependent block with tetrodotoxin and saxitoxin at frog Ranvier nodes I. Intrinsic channel and toxin parameters

The use-dependent phasic blockage of sodium channels by tetrodotoxin (TTX) and saxitoxin (STX) was examined in frog nodes of Ranvier using trains of depolarizing pulses. The decline of the peak Na⁺ current from its initial value (I ₀) before the train to a stationary value (I ) after the train was more pronounced at more negative holding potentials. The relationship betweenI /I ₀ and holding potential was fitted by a sigmoid function which yielded values for the steepness of the voltage dependencies of around –15 mV for TTX and – 8 mV for STX. Similar values were obtained at toxin concentrations of 4 and 8 nM. The higher voltage sensitivity of STX versus TTX is interpreted in terms of the higher charge and the faster binding kinetics of STX. These differences also explain the frequency dependence of the decline of Na⁺ currents with STX (between 0.5 and 2 Hz) and the frequency independence with TTX. Variation of the pulse amplitude in a train of conditioning pulses revealed that the magnitude of the use-dependent actions of STX parallels the steady-state Na⁺ inactivation curveh . Inhibition of inactivation, by pre-treatment with chloramine-T, did not, however, abolish the use dependence. Instead, it introduced a change in the time constants of the decline of the Na⁺ currents and the magnitude became independent of the holding potential.     

Age and growth of the blacknose shark, <Emphasis Type="Italic">Carcharhinus acronotus</Emphasis>, in the western North Atlantic Ocean with comments on regional variation in growth rates

We examined the age and growth of the blacknose shark, Carcharhinus acronotus, in the western North Atlantic Ocean by obtaining direct age estimates using vertebral centra. We verified annual deposition of growth increments with marginal increment analysis and validated it by analyzing vertebrae marked with oxytetracycline from a female blacknose shark held in captivity. Von Bertalanffy growth parameters indicated that female blacknose sharks have a lower growth constant (k), a larger theortical maximum size (L), and are longer lived than males. We compared these growth parameters for blacknose sharks in the western North Atlantic Ocean to growth parameters for blacknose sharks collected in the eastern Gulf of Mexico to test for differences between regions. Females in the western North Atlantic Ocean have a significantly lower L, lower k, and a higher theoretical longevity than females in the Gulf of Mexico. Males in the western North Atlantic Ocean have a higher L<>, lower k, and higher theoretical longevity than males in the Gulf of Mexico. The significant differences between these life history parameters for blacknose sharks suggest that, when possible, future management initiatives concerning blacknose sharks should consider managing the populations in the western North Atlantic and the Gulf of Mexico as separate stocks.     

Effect of extracellular pH on sodium current in isolated,single rat ventricular cells

Summary Effects of extracellular pH on the sodium current (I _Na) of single rat ventricular cells were examined under conditions of voltage clamp and internal perfusion. In this way, pH _i was controlled while pH _o was changed. The combined suction pipette-microelectrode method was used. The suction pipette passed current and perfused the cell's interior; the microelectrode measured membrane potential. Increasing extracellular H⁺ depressedI _Na and slowed inactivation. The current-voltage curves forI _Na and Slowed inactivation. The current-voltage curves forI _Na were shifted to positive and negative potentials at low and high pH _o , respectively. Similar potential shifts were observed in both the conductance voltage curve and the steadystate inactivation voltage curve (h ). Conduction was also depressed at low pH _o . The shifts were probably due to surface charge effects, while the impaired conduction was probably due to protonation of a site in the Na channel.     

Identification of gibberellin A20, abscisic acid,and phaseic acid from flowering Bryophyllum daigremontianum by combined gas chromatography-mass spectrometry

Summary The presence of abscisic and phaseic acid in a purified acidic extract from flowering plants of the long-short-day plant Bryophyllum daigremontianum [(R. Hamet and Perr.) Berg.] was conclusively established by combined gas chromatography-mass spectrometry (GC-MS) of their methyl esters. Gibberellin A₂₀ (GA₂₀) was identified by GC-MS of the methyl ester and the trimethylsilyl ether of the methyl ester. The following levels of the 3 compounds per kg fresh weight were estimated: Abscisic acid, 5.5 g; phaseic acid, 9.4g; gibberellin A₂₀, 0.8 g. When GA₂₀ and four other GAs were applied to Bryophyllum under shortday conditions, the order of effectiveness for induction of flower formation was: GA₂>GA₁>GA₅=GA₇>GA₂₀. The low biological activity of the native GA₂₀ is discussed.     

Effects of arachidonic acid and the other long-chain fatty acids on the membrane currents in the squid giant axon

Summary The effects of arachidonic acid and some other long-chain fatty acids on the ionic currents of the voltage-clamped squid giant axon were investigated using intracellular application of the test substances. The effects of these acids, which are usually insoluble in solution, were examined by using -cyclodextrin as a solvent. -cyclodextrin itself had no effect on the excitable membrane. Arachidonic acid mainly suppresses the Na current but has little effect on the K current. These effects are completely reversed after washing with control solution. The concentration required to suppress the peak inward current by 50% (ED₅₀) was 0.18mm, which was 10 times larger than that of medium-chain fatty acids like 2-decenoic acid. The Hill number was 1.5 for arachidonic acid, which is almost the same value as for medium-chain fatty acids. This means that the mechanisms of the inhibition are similar in both long- and medium-chain fatty acids. When the long-chain fatty acids were compared, the efficacy of suppression of Na current was about the same value for arachidonic acid, docosatetraenoic acid and docosahexaenoic acid. The suppression effects of linoleic acid and linolenic acid on Na currents were one-third of that of arachidonic acid. Oleic acid had a small suppression effect and stearic acid had almost no effect on the Na current. The currents were fitted to equations similar to those proposed by Hodgkin and Huxley (Hodgkin, A.L., Huxley, A.F. (1952)J. Physiol (London) 117:500–544) and the change in the parameters of these equations in the presence of fatty acids were calculated. The curve of the steady-state activation parameter (m ) for the Na current against membrane potential and the time constant of activation ( _m ) were shifted 10 mV in a depolarizing direction by the application of fatty acids. The time constant for inactivation ( _h ) has almost unaffected by application of these fatty acids.     

Effects of fatty acids on membrane currents in the squid giant axon

Summary The effects of fatty acids on the ionic currents of the voltage-clamped squid giant axon were investigated using intracellular and extracellular application of the test substances. Fatty acids mainly suppress the Na current but have little effect on the K current. These effects are completely reversed after washing with control solution. The concentrations required to suppress the peak inward current by 50% and Hill number were determined for each fatty acid. ED₅₀ decreased about 1/3 for each increase of one carbon atom. The standard free energy was –3.05 kJ mole^–1 for CH₂. The Hill number was 1.58 for 2-decenoic acid. The suppression effect of the fatty acids depends on the number of carbon atoms in the compounds and their chemical structure. Suppression of the Na current was clearly observed when the number of carbon atoms exceeded eight. When fatty acids of the same chain length were compared, 2-decenoic acid had strong inhibitory activity, but sebacic acid had no effect at all on the Na channel. The currents were fitted to equations similar to those proposed by Hodgkin and Huxley (J. Physiol. (London) 117:500–544, 1952) and the changes in the parameters of these equations in the presence of fatty acids were calculated. The curve of the steady-state activation parameter (m ) for the Na current against membrane potential and the time constant of activation ({ie113-1}) were shifted 20 mV in a depolarizing direction by the application of fatty acids. The time constant for inactivation ({ie113-2}) was almost no change by application of the fatty acids. The time constant for activation ({ie113-3}) of K current was shifted 20 mV in a depolarizing direction by the application of the fatty acids.     

Mirogrex terraesanctae (Cyprinidae) of Lake Kinneret: biomass changes in relation to inflow; growth rate in relation to fish/zooplankton interaction

Catch analyses indicate increases in Mirogrex standing stock (exploited phase) from < 2000 tonnes in the early 1950's to > 12000 tonnes in the mid-1980's and a declining abundance after 1986. Brood strength is related to concentrations of influxed organic matter which provide larval food.Estimated von Bertalanffy growth parameters (L = 164 mm TL, K = 0.25 per yr for males; L = 198 mm, K = 0.14 for females) denote a low production/biomass ratio compared to temperate cyprinid populations, and a low rate of food consumption. From estimates of zooplankton production in recent years, an average predation of < 3 % fish weight/day is calculated. The decline in zooplankton biomass since 1970 is attributed to overgrazing by Mirogrex at high stock levels. At a lower biomass, the fish population can promote ecosystem stability.Mortality estimates from Mirogrex size distribution in a period of low exploitation were 1.5 times K-values for both males and females. Similar M/K ratios were estimated for two unexploited cyprinid stocks (Phoxinus phoxinus and Acanthobrama lissneri).     

Influence of the external concentration of potassium ions on functioning of voltage-dependent potassium channels in GH3 cells

The patch-clamp technique in a whole-cell configuration was used to study the influence of the external concentration of potassium ions on the characteristics of the voltage-dependent potassium current in the plasma membrane of GH₃ cells (a cell line isolated from the rat pituitary body tumor). The [K⁺] _out shift from 5 to 100 mM induced a monotonic increase in potassium current with a constant difference between the testing potential and potassium equilibrium potential. The dependence of an activation time constant, _n , and a steady-state activation,n, of the potassium current on [K⁺] _out is of a distinct non-monotononic character with the extremum at 20 mM. Our experiments and theoretical speculations allow us to suppose that the interaction of potassium ions with slowly relaxing charged channel-forming protein groups induced the observed effects.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 110–115, March–April, 1995.     

Effect of calcium upon sodium inactivation in the giant axon ofLoligo pealei

Summary Giant axons ofLoligo pealei were voltage clamped in artificial seawater solutions containing varying concentrations of calcium from 10 to 100mm, and the sodium conductance inactivation was measured with a series of two-pulse experiments. Theh vs. voltage curve showed a shift of about 10 mV in the depolarizing direction on the voltage axis for a tenfold increase in external calcium without substantial alteration in the slope of the voltage dependence. The kinetics of the inactivation process were found to be exponential for hyperpolarizing prepulses, but showed some indication of a sigmoidal decay for depolarizing prepulses in all calcium concentrations employed. Increasing calcium increased the delay in the sigmoidal response. The inactivation time constant _h increased as a function of calcium concentration over the potential range studied, –10 to –90 mV. The values of the rate constants _h and _h are decreased with an increase in calcium and these effects are not consistent with parallel shifts of the rate constant vs. voltage curves along the voltage axis for changes in calcium concentration.Magnesium does not behave as an equimolar substitute for calcium. The effect of a solution containing 10mm calcium and 50mm magnesium is intermediate to that of solutions containing 10 and 30mm calcium alone.Predictions of a recent model for the sodium conductance (Moore, J.W., Cox, E.B., 1976Biophys. J. 16:171) which employs calcium binding were compared with the experimental data.     

Age and Growth of the Whiskery Shark, Furgaleus macki, from Southwestern Australia

Age and growth of the whiskery shark, Furgaleus macki, from southwestern Australia were examined using vertebral ageing and tag-recapture data. The readability of bands on the vertebral centra varied markedly between individuals. Four readers were used to make band counts, with the most experienced reader having the lowest index of average percent error and the highest level of agreement with final counts. Marginal increment analysis indicated that opaque bands form in January. With parturition occurring from August to October, size data suggests that the first band is probably formed 15–17 months after birth. The age at maturity was estimated to be 4.5 years for males, and 6.5 years for females. The oldest male was 10.5 years, and oldest female was 11.5 years. Von Bertalanffy growth parameters for males were L =121.5cm fork length, K=0.423 year^–1, t ₀=–0.472 years, were L =120.7cm fork length, K=0.369 year^–1, t ₀=–0.544 years for females, and were L =118.1cm fork length, K=0.420 year^–1, t ₀=–0.491 years for combined sexes. Data from a tag recapture study were analysed using a maximum likelihood method to verify the estimates of growth parameters from vertebral ageing. Von Bertalanffy growth parameters from the tag recapture study were L =128.2cm fork length, K=0.288 year^–1, t ₀=–0.654 years. The two methods of estimating growth parameters produced similar results, with rapid growth until approximately 5 years of age, after which there was little increase in length.     

Selection of a support for immobilization of a microbial lipase for the hydrolysis of triglycerides

Baterial lipase from Staphylococcus carnosus (pLipMut2) has been immobilized on various supports in order to determine a suitable immobilization technique in terms of activity and stability, when utilized for the hydrolysis of tributyrin. The hydrophobic materials PBA Eupergit and PBA Eupergit 250L prooved to be appropriate supports, when the enzyme was crosslinked with glutaraldehyde after adsorption. No desorption of the immobilized enzyme occured during operation. The pore size of the support has a strong effect on the activity but does not influence stability.The initial activity for immobilized and soluble lipase is found to follow the Arrhenius equation at low temperature, where mass transfer does not affect reaction kinetics. Activation energies for soluble and immobilized lipase were evaluated to be 21.7 kJ mol^–1 and 60.8 kJ mol^–1, respectively.Operational stability was studied in a packed bed recirculation reactor. Thermal desactivation followed first order kinetics with a half-life of 1340 h at 10°C. Model calculations for productivity showed, that optimal temperatures for high productivity are well below the temperature of maximal activity.List of Symbols E _a [kJ mol^–1] activation energy - E _d [kJ mol^–1] activation energy of desactivation - H [–] half-number - k _d [h^–1] desactivation constant - k _d, [h^–1] constant - k _N [–] desactivation constant (number) - N [–] number of runs - p [mol dm^–3] productivity - t [h] time - t _0.5 [h] half-life - T [K] absolute temperature - V [U ml^–1] activity - V(N) [Uml^–1] activity exhibited in the n-th run - V _s,O [U ml^–1] initial activity of supernatant - V _s, [U ml^–1] activity of supernatant after immobilization - V _O [U ml^–1] initial activity - V [U ml^–1] constant - _imm [–] activity yield - [ml ml^–1] ratio of volume of support to volume of supernatant Financial support of this work by the Deutsche Forschungsgemeinschaft (SFB 145, A15) is gratefully acknowledged.     

Use of single heart cells from chick embryos for the Na+ current measurements

To record the fast Na⁺ current, spheroidal heart cells enzymatically-dispersed from 3 18-day-old chick embryos were used for voltage clamping. The peak of currents in response to voltage steps of 200 ms long from holding potentials of -90 -105 mV were measured. The current-voltage curves for the peak inward current showed U-shaped relations; the averaged peak current of about -1400 pA was observed at about -30 mV and the current reversed sign at +40 + 50 mV. Both the peak current and the reversal potential values showed marked [Na]_o- dependence, i.e. reduced by 36% and by 20 mV, respectively, for a halved [Na]_o. Tetrodotoxin (TTX) partially (10^-6 M) or completely (10^-5 M) suppressed the current. The steady-state inactivation of the current (h) was characterized by the half inactivation voltage of around -80 mV and the slope factor of -4 -8 mV. The half activation voltage and the slope factor for the steady-state activation (m) were -55 mV and 4-6 mV, respectively. The electrophysiological and pharmacological properties were similar between young (3-day-old) and old (15-18-day-old) embryonic heart cells, excepting the much smaller current and the slower onset of TTX action in young embryonic hearts.     

Do neurons have a voltage or a current threshold for action potential initiation?

The majority of neural network models consider the output of single neurons to be a continuous, positive, and saturating firing ratef(t), while a minority treat neuronal output as a series of delta pulses (t — t _i ). We here argue that the issue of the proper output representation relates to the biophysics of the cells in question and, in particular, to whether initiation of somatic action potentials occurs when a certain thresholdvoltage or a thresholdcurrent is exceeded. We approach this issue using numerical simulations of the electrical behavior of a layer 5 pyramidal cell from cat visual cortex. The dendritic tree is passive while the cell body includes eight voltage- and calcium-dependent membrane conductances.We compute both the steady-state (I ^static (V _m )) and the instantaneous (I _o (V_m)) I–V relationships and argue that the amplitude of the local maximum inI ^static (V _m ) corresponds to the current thresholdI _th for sustained inputs, while the location of the middle zero-crossing ofI _o corresponds to a fixed voltage thresholdV _th for rapid inputs. We confirm this using numerical simulations: for rapid synaptic inputs, spikes are initiated if the somatic potential exceedsV _th, while for slowly varying inputI _th must be exceeded. Due to the presence of the large dendritic tree, no charge thresholdQ _th exists for physiological input.Introducing the temporal average of the somatic membrane potential (V _m) while the cell is spiking repetitively, allows us to define a dynamic I-V relationship ^dynamic ((V _m)). We find an exponential relationship between (V _m) and the net current sunk by the somatic membrane during spiking (diode-like behavior). The slope ofI/dynamic((V _m)) allows us to define a dynamic input conductance and a time constant that characterizes how rapidly the cell changes its output firing frequency in response to a change in its input.     

Age and growth of the Australian sharpnose shark,Rhizoprionodon taylori,from north Queensland,Australia

Synopsis Age and growth were studied inRhizoprionodon taylori using specimens caught in Cleveland Bay, North Queensland, Australia. Von Bertalanffy growth parameters were estimated using three different techniques: vertebral ageing, back calculation and length frequency. Vertebrae from 138 specimens were sectioned and narrow circuli counted to estimate age. Marginal increment analysis verified that circuli were produced annually in late summer, probably as a result of stress during the mating season. The oldest female was 7 and male 6 years old. Von Bertalanffy growth parameters estimated from vertebral ageing data for males were t_O = 0.410 yr, K = 1.337, L = 652.2 mm, and for females t_O = 0.455 yr, K = 1.013 and L = 732.5 mm. Growth parameters determined by length frequency and back calculation techniques concurred with those from vertebral ageing. Growth of the 0+ age class was very rapid, averaging 140% of the size at birth in the first year. Males and females matured after only one year, the lowest age at maturity reported in the family Carcharhinidae. Annual growth increments decreased rapidly after maturity, and little growth occurred after three years.     

The problem of nonstationary ion fluxes in excitable membranes

Time-dependent electrodiffusion through a membrane is analysed within a simple model treating the boundary-layers in a consistent manner. It is shown that time-independent reversal potentials for the ion fluxes exist only under steady-state conditions. We argue that this result holds very generally. Therefore nonstationary effects like ion storage and depletion inside the membrane should not contribute to the phenomena of excitability.Glossary of Symbols A _mv [V] functional cf. Equation (3) - C membrane capacitance - d one half the thickness of the membrane - F[V] functional cf. Equation (1) - g _i electrochemical potential inside membrane - g _i electrochemical potentials outside membrane at x ±d, respectively - i (index) refers to i-th ionic species - J electric current across membrane - j = j ^} = j ^< current density measured by external electrodes - j _i (x) current density inside membrane in x-direction - j _i ^inst(x) instantaneous current density - J _i ^stat steady-state current density - k Boltzmann constant - m (index) is used in Sec. 2 to denote the independent diffusion currents - n ^< ionic strength of electrolyte at x = - - n _i density of ions inside membrane - n _i density of ions outside membrane at x = ±, respectively - Q charge per unit area of boundary layers at x ± d, respectively - Q ₀ fixed charge per unit area of membrane - q elementary charge - q _i ionic charges - T temperature - it time - V membrane potential (= (-)-()) - V _i Nernst potential - V potential drops inside boundary layers (can be neglected, see Appendix II) - V ^± potential steps at x = ± d, cf. Equation (29) - V ₀ = V ^–-V ⁺ - w _i activation energy inside membrane - x spatial coordinate perpendicular to membrane - y, z spatial coordinates parallel to membrane - dielecric constant - ₀ dielectric constant of electrolyte solution ( 80) - _m dielectric constant of membrane ( 5) - (x) electrostatic potential - charge density of boundary layers - ⁰ fixed charge density inside membrane - spatial average, cf. Equation (12)     

Existence and uniqueness of a sharp travelling wave in degenerate non-linear diffusion Fisher-KPP equations

In this paper we use a dynamical systems approach to prove the existence of a unique critical value c ^* of the speed c for which the degenerate density-dependent diffusion equation u _ct = [D(u)u _x ] _x + g(u) has: 1. no travelling wave solutions for 0 < c < c ^*, 2. a travelling wave solution u(x, t) = (x - c ^* t) of sharp type satisfying (– ) = 1, () = 0 ^*; '(^*–) = – c ^*/D'(0), '(^*+) = 0 and 3. a continuum of travelling wave solutions of monotone decreasing front type for each c > c ^*. These fronts satisfy the boundary conditions (– ) = 1, '(– ) = (+ ) = '(+ ) = 0. We illustrate our analytical results with some numerical solutions.     

Miniemulsion as efficient system for enzymatic synthesis of acid alkyl esters

The aim of this work is to devise an efficient enzymatic process for the production of linear alkyl esters in aqueous miniemulsion systems. The esterification reactions of linear alcohols and carboxylic acids were performed with three different enzymes, commercial Amano lipase PS from Pseudomonas cepacia, Lipase type VII from Candida rugosa, and lyophilized Fusarium solani pisi cutinase expressed in Saccharomyces cerevisiae SU50. The miniemulsion system shows a high potential for the synthesis of linear alkyl esters, for example, hexyl octanoate, which could be synthesized with an ester yield of 94% using Amano lipase PS. Even with hydrophilic alcohols as ethanol, ethyl decanoate could be obtained with a concentration of 0.45 M and a yield of 62% using F. s. pisi cutinase as catalyst. High esterification rates for ethyl‐ and hexyloleate in miniemulsion showed a significant shift in cutinase selectivity towards longer chain length carboxylic acids. The stepwise addition of the alcohol led to an increase of the esterification yield. Moreover, increasing the amount of dispersed organic phase, mainly consisting of the substrates, led to a significant increase of the final ester concentration (e.g., concentration of 1.4 M for ethyl decanoate for the esterification with Amano Lipase PS). Biotechnol. Bioeng. 2010;106: 507–515. © 2010 Wiley Periodicals, Inc.     

Some effects of short-chain phospholipids and n-alkanes on a transient potassium current (I A ) in identified Helix neurons

Many effects of short-chain phospholipids and n-alkanes on the squid axon sodium current (I _Na) are consistent with mechanisms involving changes in membrane thickness. Here, we suggest that the actions of short-chain phospholipids on an A-type potassium current (I _A ) in two-microelectrode voltage clamped Helix D1 and F77 neurons are incompatible with such simple mechanisms. Diheptanoyl phosphatidylcholine (diC₇PC, 0.2 and 0.3 mm) caused substantial (58 and 79%), and in some cases partially reversible, increases in I _A amplitude. These were correlated with hyperpolarizing shifts of up to –7 mV in the voltage dependence of current activation. The voltage dependence of steady-state inactivation was also moved in the hyperpolarizing direction. These effects are the opposite of those described for squid I _Na. 0.5 Saturated n-pentane and saturated n-hexane caused significant (–3 and –6 mV) hyperpolarizing shifts in the voltage dependence of I _A inactivation, qualitatively consistent with their effects on squid I _Na, while the voltage dependence of activation was moved slightly to the left or unchanged. Hydrocarbons had variable effects on peak current amplitude, although saturated n-pentane produced a clear suppression. DiC₇PC caused a 25% increase in the time constant of macroscopic I _A inactivation ( _b ) but 0.5 saturated n-pentane and saturated n-hexane reduced _b by 40%. The effects of these agents on current-clamped cells were broadly consistent with their opposing actions on _b —phospholipids tended to reduce excitability and n-alkanes tended to increase it. Possible mechanisms of I _A perturbation are discussed.We gratefully acknowledge financial support from the Science and Engineering Research Council and the Wellcome Trust. We would also like to thank Prof. H. Meves, Dr. N. Franks and Dr. W. Lieb for helpful discussions.