Male gamete chemotaxis towards the female gamete is a general strategy to facilitate the sexual reproduction in many marine eukaryotes. Biochemical studies of chemoattractants for male gametes of brown algae have advanced in the 1970s and 1980s, but the molecular mechanism of male gamete responses to the attractants remains elusive. In sea urchin, a K+ channel called the tetraKCNG channel plays a fundamental role in sperm chemotaxis and inhibition of K+ efflux through this channel by high K+ seawater blocks almost all cell responses to the chemoattractant. This signalling mechanism could be conserved in marine invertebrates as tetraKCNG channels are conserved in the marine invertebrates that exhibit sperm chemotaxis. We confirmed that high K+ seawater also inhibited sperm chemotaxis in ascidian, Ciona intestinalis (robusta), in this study. Conversely, the male gamete chemotaxis towards the female gamete of a brown alga, Mutimo cylindricus, was preserved even in high K+ seawater. This result indicates that none of the K+ channels is essential for male gamete chemotaxis in the brown alga, suggesting that the signalling mechanism for chemotaxis in this brown alga is quite different from that of marine invertebrates. Correlated to this result, we revealed that the channels previously proposed as homologues of tetraKCNG in brown algae have a distinct domain composition from that of the tetraKCNG. Namely, one of them possesses two repeats of the six transmembrane segments (diKCNG) instead of four. The structural analysis suggests that diKCNG is a cyclic nucleotide-modulated and/or voltage-gated K+ channel.

Drug delivery systems (DDSs) have been developed to target tumor cells by releasing active biomolecules at the specific site of infection, thus eliminating the side effects of anticancer drugs. However, DDSs are generally limited by high drug dosage, biobarriers, poor target recognition, etc. To address these deficiencies, we propose a new noninvasive method consisting of exposing the cancer cells to a combination of low-intensity pulsed ultrasound (LIPUS) and static magnetic field (SMF). This combined treatment found to negatively regulate colon cancer cell (HCT116) activities in vitro by altering their cell membrane potential and permeability thus increased the DDS efficacy by 40%. The treated cancer cell membrane became hyperpolarized leading to cancer cell death. The combination treatment (LIPUS + SMF) restricted the cancer cell proliferation to 16 and 5% in the presence of bare anticancer drug and DDS, respectively, in 72 h, which is almost 40% higher than that observed without the treatment. The acceleration of cancer cellular inhibition was confirmed by the significant increase in the apoptosis of the cell exposed to the LIPUS + SMF treatment. The observed improvement is believed to be due to changes in the cell membrane stability/permeability as a result of mechanical (20–22 kPa) and electrical (19–23 µV/cm) stimuli generated during the LIPUS + SMF treatment.

The aryloxyphenoxypropionate and cyclohexanedione herbicides, which inhibit acetyl-coenzyme A carboxylase (EC 6.4.1.2), have also been hypothesized to act at specific sites on the plasmalemma. An impermeant sulfhydryl binding agent was reported to block the diclofop acid-induced depolarization of the membrane potential (Em) in rigid ryegrass. A correlation between the antagonistic interaction with auxin herbicides both in the field and in the Em response, and the repolarization of Em in herbicide-resistant rigid ryegrass following removal of diclofop acid also provide support for this hypothesis. However, similar membrane responses in resistant grasses and broadleaf species suggest that the membrane response may not be important in the phytotoxic activity of the postemergence graminicides under field conditions. In addition, an antagonistic interaction was not observed in roots of susceptible grasses exposed to combinations of diclofop-methyl and 2,4-D. Furthermore, the repolarization of the Em in diclofop-resistant rigid ryegrass was correlated to differential acidification of the external solution and an increase in the protonated form of diclofop acid, rather than a site-specific interaction at the plasmalemma. Although the membrane response is probably not involved in herbicide phytotoxicity in agricultural systems, a higher extracellular pH in the resistant biotypes of rigid ryegrass may inhibit the movement of these weak-acid herbicides across the plasmalemma, and possibly contribute to increased herbicide tolerance.

Oxidative stress and mitochondrial failure promote altered protein degradation, reduced neurotransmission, synapse loss and tau/hyperphosphorylation, which are early stages in the development of Alzheimer's disease (AD). A growing volume of data confirms that Ginkgo biloba extract (GBE) reduces oxidative stress and improves mitochondrial respiration and thus may be useful in preventing or slowing down the progression of AD. Treatment of Caenorhabditis elegans with GBE- extract reduces oxidative stress and extends median lifespan compared with controls. Levels of reactive oxygen species, including the superoxide anion radical, were reduced in brains from GBE-treated mice compared with controls. In older mice, GBE resulted in a protective effect by increasing production of adenosine triphosphate in neurons. A respiratory experiment indicated that GBE was able to rescue Aβ-induced defects in energy metabolism, with results suggesting long-term regulatory effects on mitochondria. GBE also had a selective effect on the activities of mitochondrial enzymes that assemble the electron transport system. The flavonoids, bilobalide and some of the ginkgolides (B and J) had a high protective capacity, indicating that a combination of several compounds within standardized Gingko biloba extracts contribute disproportionately for these protective effects.

The intrategumental pH in adult male Schistosoma mansoni as measured with pH-sensitive microelectrodes is between 7.0 and 7.2, a value about one pH unit more alkaline than expected for equilibrium. This value is maintained for at least 4 h after isolation in media buffered with Hepes or CO2/ with or without serum present. CCCP (1 μM) and FCCP (10 μM) cause rapid acidification. DNP (1 mM) and Na-orthovanadate (1 mM) acidify but also cause significant depolarization of the tegument. NH (20 mM) depolarizes and acidifies the tegument with no evidence of transient alkalinization. High K+ (25 mM) accelerates the acidification. Removal of the NH+4 causes a large transient further acidification with recovery requiring as long as 40 min. High K+ (25 mM) delays the early stage of the recovery. Presence of CO2/HCO in the incubation medium does not accelerate the recovery rate nor does SITS (100 μM) inhibit the recovery. Intrategumental Na+ is elevated after an acid load and amiloride (3 mM) as well as low Na+ medium interfere with recovery from the acid load indicating that a Na+–H+ exchanger may be present in the tegumental membrane.

The cellular oxygen sensing system of the body ensures appropriate adaptation of cellular functions toward hypoxia by regulating gene expression and ion channel activity. Two-photon laser microscopy is an ideal tool to study and prove the relevance of the molecular mechanisms within oxygen sensing pathways on the cellular and complex tissue or organ level. Images of hypoxia inducible factor 1 (HIF-1) subunit nuclear mobility and protein-protein interaction in living cells, of hypoxia-induced changes in membrane potential and intracellular calcium of live ex vivo carotid bodies as well as of rat kidney proximal tubulus function in vivo, will be shown.

Second-harmonic generation (SHG) can be used for imaging membrane potential in neurons, but poor signal-to-noise (S/N) limits accurate measurements of small voltage transients. We use photon counting to improve the S/N of weak SHG signal detection. Photon counting generates shot-noise limited and integrable signals, eliminates pulse-to-pulse variation, and built-in discriminators reduces the background to practically zero. In single trials, by using photon counting, we obtain a more than a twofold S/N increase over analog voltage detection. Trial-to-trial variability is also reduced by 50%. Finally, we show that, using photon counting, the kinetics of fast events such as action potentials can be recorded more accurately.

Magnesium ions as well as calcium ions are required for successful fertilisation in sea urchins. In the absence of Mg2+ spermatozoa attached to the egg plasma membrane, their acrosomal processes passing through the vitelline envelope, but could not enter the egg cytoplasm (Sano et al, Dev. Growth Differ. 22, 531–41,1980). Such an individual spermatozoon was observed microscopically to resume entry into the egg immediately after the addition of a sufficient amount of Mg2+ to the surrounding medium. Neither any change in membrane potential nor an increase in intracellular Ca2+ concentration of the egg was observed after insemination in the absence of Mg2+, although both could be observed after the addition of Mg2+. The sperm heads did not show fluorescence when attached to the surface of an egg previously microinjected with mithramycin A in Mg-free seawater, indicating that there was no connection between the sperm and the egg. Therefore, occurrence of fertilisation potential must be a post-fusional event. These results suggest that Mg2+ are indispensable for fusion between the sperm acrosomal membrane and the egg plasma membrane.

Both the thalamocortical and limbic systems generate a variety of brain state-dependent rhythms but the relationship between the oscillatory families is not well understood. Transfer of information across structures can be controlled by oscillations. We suggest that slow oscillation of the neocortex, which was discovered by Mircea Steriade, temporally coordinates the self-organized oscillations in the neocortex, entorhinal cortex, subiculum and hippocampus. Transient coupling between rhythms can guide bidirectional information transfer among these structures and might serve to consolidate memory traces.

The fatigue of high-intensity exercise is now believed to reside primarily within the excitation–contraction coupling processes associated with the plasma membrane of skeletal muscle (sarcolemm) and calcium-mediated events leading to myofilament sliding. This paper summarizes recent developments and advances in the identification of factors that contribute to changes in sarcolemmal excitability of mammalian skeletal muscle as a consequence of high-intensity exercise. There is an increasing recognition of the probable role that is played by the transverse tubular system (T-system), a system that comprises c. 80% of the total sarcolemmal surface capable of ion exchange. Furthermore, the fluid within the T-system has limited access to interstitial fluid bathing myofibres; hence, T-system fluid is probably markedly different from interstitial fluid during high-intensity exercise. Mechanically skinned fibre preparation is providing many new insights into functions of the surface membrane and T-system in fatigue. A scenario is developed whereby accumulation of potassium within the T-system ([K+]o) contributes to reduced membrane excitability, as well as lowering of T-system sodium and chloride, concomitant with loss of intracellular potassium ([K+]i) and accumulation of intracellular sodium ([Na+]) and chloride ([Cl−]). Lowering the [Na+]o/[Na+]i ratio and raising myoplasmic [Na+]i have been shown to decrease membrane excitability and impair action potential propagation. Maintained high [Cl−]o may also have a protective effect in maintaining membrane excitability, and this effect appears to be very pronounced in the presence of raised [K+]o. In contrast to dogma associating high [H+] to fatigue, recent studies have also shown that induced acidosis that results in increased [H+]o and [H+]i restores force production in muscles and skinned fibres fatigued by intermittent tetanic stimulation. This effect may be due to a decrease in surface membrane Cl− permeability that serves to restore membrane excitability. During high-intensity exercise, simultaneous changes in trans-membrane ion concentrations and membrane ion conductances may serve to reduce impairment of membrane excitability that provides for a maintained, though reduced, contractile function.

Uptake of the lipophilic cation, tetraphenylphosphonium (TPP+), which is often used as a membrane potential probe, was studied in the cyanobacterium Synechococcus R-2 (PCC 7942) to determine if the technique was valid for these cells. Lipophilic cation probes are notorious for giving inconsistent estimates of membrane potential (ΔΨ) using the Nernst equation (ETPP+=ΔΨ). It is necessary to correct for the large amounts of TPP+ bound to the surface of the cells. The rate of equilibration of intracellular TPP+ is very fast (t½≈1–3 min), hence the permeability of the plasmalemma to TPP+ (PTPP+≈10–50 nm s−1) is very high. There appears to be an active uptake of TPP+ with a pH optimum at about pHo 7.5. TPP+ does not readily uncouple Synechococcus cells. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and dinitrophenol depolarized ETPP+, but monensin made ETPP+ more negative. Accumulation of TPP+ is not affected by [K+] in the medium in a way consistent with it acting as a reporter of the membrane potential. Addition of K+, NH4+ and HCO3− altered the uptake rate of TPP+ in a way consistent with electrogenic uptake of these ions but the effects were smaller than those found using the 86Rb+/valinomycin and 201TI+ probes. A comparison has been made with ΔΨ determinations using other membrane potential probes. ETPP+ was often close to the value of the membrane potential obtained using other methods under control conditions but effects of experimental treatments are sometimes inconsistent with those found using other ΔΨ probes. The TPP+ method is therefore unreliable and could be seriously misleading.

The effect of hypoxic exposure on in vitro duodenal Fe uptake kinetics was studied in tissue fragments from rats that were fed or fasted overnight before study. Hypoxic exposure was for 3 d at 0·5 atm and fasting was for the last 18-24 h before Fe uptake determinations. The non-permeable Fe2+ chelator 3-(2-pyridyl)-5,6-bis-(4-phenyl-sulphonic acid)-l,2,4-triazine (ferrozine), and medium deoxygenation inhibited uptake in all experimental groups. Ferrozine sensitivity and mucosal Fe3+ reductase activity were greatest in hypoxic animals. Fe uptake was inhibited by membrane depolarization only after fasting or hypoxic exposure of the rats. The data demonstrated that Fe uptake by rat duodenal fragments involves at least two mechanisms: a membrane-potentialindependent mechanism which is not responsive to hypoxia and a second mechanism, induced by fasting or hypoxia, which is inhibited by membrane depolarization. Uptake is partially dependent on reduction of Fe3+ to Fe2+ and this is primarily associated with the second mechanism for uptake. These properties have been reported also in mouse and human Fe uptake, suggesting that the rat is a useful model for the study of basic mechanisms of Fe absorption