Haemoglobin expression in in vivo murine preimplantation embryos suggests a role in oxygen-regulated gene expression.

Haemoglobin expression is not restricted to erythroid cells. We investigated the gene expression of the haemoglobin subunits haemoglobin, alpha adult chain 1 (Hba-a1) and haemoglobin, beta (Hbb), 2,3-bisphosphoglycerate mutase (Bpgm) and the oxygen-regulated genes BCL2/adenovirus E1B interacting protein 3 (Bnip3), solute carrier family 2 (facilitated glucose transporter), member 1 (Slc2a1) and N-myc downstream regulated gene 1 (Ndrg1) in the murine preimplantation embryo, comparing invivo to invitro gene expression. Relatively high levels of Hba-a1 and Hbb were expressed invivo from the 2-cell to blastocyst stage; in contrast, little or no expression occurred invitro. We hypothesised that the presence of haemoglobin invivo creates a low oxygen environment to induce oxygen-regulated gene expression, supported by high expression of Slc2a1 and Ndrg1 in invivo relative to invitro embryos. In addition, analysis of an invitro-derived human embryo gene expression public dataset revealed low expression of haemoglobin subunit alpha (HBA) and HBB, and high expression of BPGM. To explore whether there was a developmental stage-specific effect of haemoglobin, we added exogenous haemoglobin either up to the 4-cell stage or throughout development to the blastocyst stage, but observed no difference in blastocyst rate or the inner cell mass to trophectoderm cell ratio. We conclude that haemoglobin in the invivo preimplantation embryo raises an interesting premise of potential mechanisms for oxygen regulation, which may influence oxygen-regulated gene expression.

Artificial blastocyst collapse prior to vitrification significantly improves Na+/K+-ATPase-dependent post-warming blastocoel re-expansion kinetics without inducing endoplasmic reticulum stress gene expression in the mouse.

Blastocoel expansion during embryo development is known to be reliant on the Na+/K+-ATPase pump, but little is known about the relative contribution of active (Na+/K+-ATPase pump) and facilitated diffusion (aquaporins) water transport during blastocoel re-expansion after vitrification. The aims of this study were to examine potential effects of artificial blastocoel collapse (ABC) on markers of embryo stress and the contribution of active and facilitated diffusion water transport mechanisms to blastocoel re-expansion. Day 5 mouse embryos were vitrified using either a standard protocol, laser pulse ABC, a hyperosmotic sucrose ABC protocol or both laser pulse and sucrose. Using real-time polymerase chain reaction, no differences were found in the gene expression of the endoplasmic reticulum (ER) stress markers activating transcription factor 4 (Atf4) or heat shock protein 90-alpha (Hsp90α) 2h after warming. Similarly, expression of the Na+/K+-ATPase pump gene, ATPase, Na+/K+ transporting, beta 1 polypeptide (Atp1b1) and protein did not differ between groups. Aquaporin 8 (Aqp8) gene expression was significantly lower in the laser+sucrose ABC group than in fresh controls, and aquaporin 3 (Aqp3) expression significantly higher in standard vitrified embryos compared with all other groups. Ouabain, a potent and specific Na+/K+-ATPase pump inhibitor, inhibited blastocoel re-expansion in both standard protocol- and laser ABC-vitrified embryos, reducing both groups to the same rate of re-expansion 3h after warming. These results demonstrate that ABC before vitrification does not alter mRNA or protein expression of Na+/K+-ATPase, or mRNA levels of ER stress genes Atf4 and Hsp90α. Activity of the pump may be increased in ABC embryos, with potential compensation by AQP3 when it is compromised.

Evaluation of the effectiveness and usability of an educational portion size tool, ServARpreg, for pregnant women.

BACKGROUND: Elevated blood glucose levels in pregnancy increases the risk of adverse pregnancy outcomes. Modifying consumption of carbohydrate-rich foods is important for blood glucose regulation; however, the tools commonly used to assist in guiding portion control are impractical. The present study aimed to evaluate usability of ServARpreg, a mobile phone-based nutrition tool, and its effectiveness with respect to improving carbohydrate and standard serve size knowledge in pregnant women. METHODS: A baseline survey assessed knowledge of carbohydrates and standard serve sizes of pregnant women. A subset of women living in Newcastle were invited to use ServARpreg, containing pregnancy nutrition information and augmented reality guidance on portion control. A follow-up survey was sent to all women 4 weeks after baseline and women who received ServARpreg also received a process evaluation survey after 10 weeks. RESULTS: Responses were received from 186 pregnant women for the baseline survey, with 97 completing the follow-up (52.2%). Of the 56 women eligible to receive ServARpreg in the sub-study, 47 accepted (83.9%) and, of these, 40 completed the process evaluation survey (85.1%). At follow-up, there was a significant group × time interaction in favour of the ServARpreg group for carbohydrate quantification knowledge (F1,279  = 9.705, P = 0.002). Standard serve size knowledge did not change between groups. In the process evaluation survey, 80% strongly agreed/agreed that ServARpreg made them more aware of how much they ate and 72.5% found ServARpreg easy to use. CONCLUSIONS: ServARpreg has shown potential to educate pregnant women about carbohydrate quantification and increase portion size awareness. Further refinement of the tool and evaluation is needed to improve standard serve size knowledge.

The current state of reproductive biology research in Australia and New Zealand: core themes from the Society for Reproductive Biology Annual Meeting, 2016.

Because reproduction is essential for all life, it is central to our understanding of all aspects of biology. The Society for Reproductive Biology (SRB) 2016 conference held on the Gold Coast (Qld, Australia) displayed the current breadth of reproductive research in Australia and New Zealand, with additional insights from world leaders in the field. This conference review provides a focused summary of the key questions, emerging ideas and novel technologies that were presented in the symposia. Presented research demonstrated key advances in how stem cell biology may allow us to better understand pluripotency, as well as how environmental and lifestyle factors, such as circadian disruption, smoking, alcohol and diet, affect gametogenesis, embryo implantation, placental function and reproductive capacity. Sessions also highlighted the role of reproductive biology in providing insight into the mechanisms and processes governing a wide range of biological science disciplines, including cancer research and therapies, oncofertility, conservation of native species and chronic non-communicable diseases. Recurring themes included the importance of male and female gamete quality for reproductive potential and the critical and varied roles of the placenta in the maintenance of a healthy pregnancy. Dysregulation of reproductive processes can contribute to a variety of pathological states that affect future health, fertility and fecundity. Research being conducted by the SRB has the potential to shape not only the fertility of the current generation, but also the health and reproductive viability of future generations.

Long-term epidemiological survey of Kudoa thyrsites (Myxozoa) in Atlantic salmon (Salmo salar L.) from commercial aquaculture farms.

Kudoa thyrsites (Myxozoa) encysts within myocytes of a variety of fishes. While infected fish appear unharmed, parasite-derived enzymes degrade the flesh post-mortem. In regions of British Columbia (BC), Canada, up to 4-7% of fillets can be affected, thus having economic consequences and impacting the competitiveness of BC's farms. K. thyrsites was monitored in two farms having high (HP) or low (LP) historical infection prevalence. At each farm, 30 fish were sampled monthly for blood and muscle during the first year followed by nine samplings during year two. Prevalence and intensity were measured by PCR and histology of muscle samples. In parallel, fillet tests were used to quantify myoliquefaction. Infections were detected by PCR after 355 and 509 degree days at LP and HP farms, respectively. Prevalence reached 100% at the HP farm by 2265 degree days and declined during the second year, whereas it plateaued near 50% at the LP farm. Infection intensities decreased after 1 year at both farms. Blood was PCR-positive at both farms between 778 and 1113 degree days and again after 2000 degree days. This is the first monitoring project in a production environment and compares data between farms with different prevalence.

Hyperglycaemic conditions perturb mouse oocyte in vitro developmental competence via beta-O-linked glycosylation of heat shock protein 90.

STUDY QUESTION: What is the effect of beta-O-linked glycosylation (O-GlcNAcylation) on specific proteins in the cumulus-oocyte complex (COC) under hyperglycaemic conditions? SUMMARY ANSWER: Heat shock protein 90 (HSP90) was identified and confirmed as being O-GlcNAcylated in mouse COCs under hyperglycaemic conditions (modelled using glucosamine), causing detrimental outcomes for embryo development. WHAT IS KNOWN ALREADY: O-GlcNAcylation of proteins occurs as a result of increased activity of the hexosamine biosynthesis pathway, which provides substrates for cumulus matrix production during COC maturation, and also for O-GlcNAcylation. COCs matured under hyperglycaemic conditions have decreased developmental competence, mediated at least in part through the mechanism of increased O-GlcNAcylation. STUDY DESIGN, SIZE, DURATION: This study was designed to examine the effect of hyperglycaemic conditions (using the hyperglycaemic mimetic, glucosamine) on O-GlcNAc levels in the mouse COC, and furthermore to identify potential candidate proteins which are targets of this modification, and their roles in oocyte maturation. PARTICIPANTS/MATERIALS, SETTING, METHODS: COCs from 21-day-old superovulated CBA × C57BL6 F1 hybrid female mice were matured in vitro (IVM). Levels of O-GlcNAcylated proteins, HSP90 and O-GlcNAc transferase (OGT, the enzyme responsible for O-GlcNAcylation) in COCs were measured using western blot, and localization observed using immunocytochemistry. For glycosylated HSP90 levels, and to test OGT-HSP90 interaction, immunoprecipitation was performed prior to western blotting. Embryo development was assessed using in vitro fertilization and embryo culture post-maturation. MAIN RESULTS AND THE ROLE OF CHANCE: Addition of the hyperglycaemic mimetic glucosamine to IVM medium for mouse COCs increased detectable O-GlcNAcylated protein levels (by western blot and immunocytochemistry), and this effect was reversed using an OGT inhibitor (P < 0.05). HSP90 was identified as a target of O-GlcNAcylation in the COC, and inhibition of HSP90 during IVM reversed glucosamine-induced decreases in oocyte developmental competence (P < 0.05). We also demonstrated the novel finding of an association between HSP90 and OGT in COCs, suggesting a possible client-chaperone relationship. LIMITATIONS, REASONS FOR CAUTION: In vitro maturation of COCs was used so that treatment time could be limited to the 17 h of maturation prior to ovulation. Additionally, glucosamine, a hyperglycaemic mimetic, was used because it specifically activates the hexosamine pathway which provides the O-GlcNAc moieties. The results in this study should be confirmed using in vivo models of hyperglycaemia and different HSP90 inhibitors. WIDER IMPLICATIONS OF THE FINDINGS: This study leads to a new understanding of how diabetes influences oocyte competence and provides insight into possible therapeutic interventions based on inhibiting HSP90 to improve oocyte quality. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by a programme grant from the National Health and Medical Research Council, Australia, ID 453556. J.G.T. is a recipient of funding from and a consultant to Cook Medical Pty Ltd. The other authors have no conflicts of interest to declare.

Short oestrous cycles in sheep during anoestrus involve defects in progesterone biosynthesis and luteal neovascularisation.

Anoestrous ewes can be induced to ovulate by the socio-sexual, 'ram effect'. However, in some ewes, the induced ovulation is followed by an abnormally short luteal phase causing a so-called 'short cycle'. The defect responsible for this luteal dysfunction has not been identified. In this study, we investigated ovarian and uterine factors implicated in male-induced short cycles in anoestrous ewes using a combined endocrine and molecular strategy. Before ovulation, we were able to detect a moderate loss of thecal expression of steroid acute regulatory protein (STAR) in ewes that had not received progesterone priming (which prevents short cycles). At and following ovulation, we were able to identify a significant loss of expression of genes coding key proteins involved in the biosynthesis of progesterone (STAR, CYP11A1 and HSD3B1 (HSD3B)) as well as genes coding proteins critical for vascular development during early luteal development (VEGFA and KDR (VEGFR2)), suggesting dysfunction in at least two pathways critical for normal luteal function. Furthermore, these changes were associated with a significant reduction of progesterone production and luteal weight. Additionally, we cast doubt on the proposed uterus-mediated effect of prostaglandin F2α (PGF2α) as a cause of short cycles by demonstrating the dysregulation of luteal expression of the PGF receptor, which mediates the luteal effects of PGF2α, and by finding no significant changes in the circulating concentrations of PGFM, the principal metabolite of PGF2α in ewes with short cycles. This study is the first of its kind to examine concurrently the endocrine and molecular events in the follicular and early luteal stages of the short cycle.

Cognitive content specificity in anxiety and depressive disorder symptoms: a twin study of cross-sectional associations with anxiety sensitivity dimensions across development.

BACKGROUND: The classification of anxiety and depressive disorders has long been debated and has important clinical implications. The present study combined a genetically sensitive design and multiple time points to investigate cognitive content specificity in anxiety and depressive disorder symptoms across anxiety sensitivity dimensions, a cognitive distortion implicated in both disorders. METHOD: Phenotypic and genetic correlations between anxiety sensitivity dimensions, anxiety and depressive disorder symptoms were examined at five waves of data collection within childhood, adolescence and early adulthood in two representative twin studies (n pairs = 300 and 1372). RESULTS: The physical concerns dimension of anxiety sensitivity (fear of bodily symptoms) was significantly associated with anxiety but not depression at all waves. Genetic influences on physical concerns overlapped substantially more with anxiety than depression. Conversely, mental concerns (worry regarding cognitive control) were phenotypically more strongly associated with depression than anxiety. Social concerns (fear of publicly observable symptoms of anxiety) were associated with both anxiety and depression in adolescence. Genetic influences on mental and social concerns were shared to a similar extent with both anxiety and depression. CONCLUSIONS: Phenotypic patterns of cognitive specificity and broader genetic associations between anxiety sensitivity dimensions, anxiety and depressive disorder symptoms were similar at all waves. Both disorder-specific and shared cognitive concerns were identified, suggesting it is appropriate to classify anxiety and depression as distinct but related disorders and confirming the clinical perspective that cognitive therapy is most likely to benefit by targeting cognitive concerns relating specifically to the individual's presenting symptoms across development.

The pattern of LH secretion and the ovarian response to the 'ram effect' in the anoestrous ewe is influenced by body condition but not by short-term nutritional supplementation.

In sheep, the 'ram effect' induces out-of-season fertility and good nutrition increases prolificacy. This experiment determined if fatness or short-term nutritional supplementation modified the response to the 'ram effect'. A group of 48 Île-de-France ewes were fed diets that produced groups with body-condition scores (BCS) of >3.0 and <2.0. Within each BCS group animals were supplemented daily with 500g of lupins from Day -5 to Day 0 (ram introduction) resulting in four groups: low BCS, supplemented (n=7) and non-supplemented (n=8) and high BCS, supplemented (n=12) and non-supplemented (n=11). The blood concentrations of glucose and insulin and the LH response to gonadotrophin-releasing hormone (GnRH) were determined. After the 'ram effect' the pattern of LH pulsatility, the LH surge and ovarian responses were analysed. Low BCS ewes had lower glucose and insulin (P<0.001) and supplementation increased both (P≤0.001). The increase in LH induced by GnRH was reduced in low BCS ewes (P=0.015) but it was not affected by supplementation. Similarly, LH pulsatility was reduced in low BCS ewes (P<0.05). The LH surge and ovarian cyclicity were not affected but the follow-up cycle was delayed (P=0.034) and progesterone was reduced (P=0.029) in low BCS ewes. There was an effect of BCS on ovulation rate (P<0.05). These results show that the BCS can modify the response to the 'ram effect' and that supplementation has little effect on this response.

Nutritional and metabolic mechanisms in the ovary and their role in mediating the effects of diet on folliculogenesis: a perspective.

Folliculogenesis in ruminants is a nutritionally sensitive process, and short-term increases in nutrient flux can stimulate folliculogenesis in sheep and cattle. These short-term effects are probably mediated directly at the follicular level to modify gonadotrophin-induced follicle growth and development. The follicle appears to have a number of 'nutrient sensing' mechanism that may form the link between nutrient status and folliculogenesis. This review examines the evidence for the presence of pathways that may sense nutrient flux from within the follicle including the insulin signalling pathway, adenosine monophosphate-activated kinase (AMPK), the hexosamine pathway, peroxisome proliferator-activated receptors (PPARs) and leptin. The review then assesses the available evidence concerning their mechanisms in the follicle and speculates on how these 'nutrient sensing' pathways are integrated into the FSH signalling pathways to adjust gonadotrophin-stimulated follicular function. We conclude that there is good evidence to suggest that the follicle does contain more than one functional 'nutrient sensing' pathway that have intra-follicular effects on some FSH-mediated functions such as the synthesis of oestradiol, in granulosa cells. These pathways include insulin, AMPK, and leptin. There is also a good case for the integration of PPARs in the intra-follicular sensing of nutrient flux. However, there is little evidence at present to suggest the hexosamine biosynthetic pathway has functional significance in the follicle as a sensor of nutrient flux. Further study will be required to fully understand 'nutrient sensing' pathways in the follicle and their cross-talk with FSH signalling pathways.

The bipolar kinesin, KLP61F, cross-links microtubules within interpolar microtubule bundles of Drosophila embryonic mitotic spindles.

Previous genetic and biochemical studies have led to the hypothesis that the essential mitotic bipolar kinesin, KLP61F, cross-links and slides microtubules (MTs) during spindle assembly and function. Here, we have tested this hypothesis by immunofluorescence and immunoelectron microscopy (immunoEM). We show that Drosophila embryonic spindles at metaphase and anaphase contain abundant bundles of MTs running between the spindle poles. These interpolar MT bundles are parallel near the poles and antiparallel in the midzone. We have observed that KLP61F motors, phosphorylated at a cdk1/cyclin B consensus domain within the BimC box (BCB), localize along the length of these interpolar MT bundles, being concentrated in the midzone region. Nonphosphorylated KLP61F motors, in contrast, are excluded from the spindle and display a cytoplasmic localization. Immunoelectron microscopy further suggested that phospho-KLP61F motors form cross-links between MTs within interpolar MT bundles. These bipolar KLP61F MT-MT cross-links should be capable of organizing parallel MTs into bundles within half spindles and sliding antiparallel MTs apart in the spindle midzone. Thus we propose that bipolar kinesin motors and MTs interact by a "sliding filament mechanism" during the formation and function of the mitotic spindle.

Ionic basis of the photoresponse of Aplysia giant neuron: K + permeability increase.

The giant neuron of the Aplysia abdominal ganglion hyperpolarizes during illumination. The light-initiated potential change is associated with an increase of membrane conductance. It reverses sign at the potassium equilibrium potential (about -83 millivolts), which was determined from direct measurements of internal potassium activity. The membrane hyperpolarization is produced entirely by a light-induced increase in potassium permeability.

Current-voltage relations during illumination: photoreceptor membrane of a barnacle.

In voltage clamped photoreceptor cells of the barnacle, light-induced membrane current varied nonlinearly with membrane potential and changed sign at about + 27 millivolts (reversal potential) independently of light intensity. Instantaneous current-voltage relations were linear and intersected the voltage axis at the reversal potential. Illumination increased membrane conductance that was dependent on membrane potential, light intensity, and time.

Tissue-specific progesterone receptor-chromatin binding and the regulation of progesterone-dependent gene expression.

Progesterone receptor (PGR) co-ordinately regulates ovulation, fertilisation and embryo implantation through tissue-specific actions, but the mechanisms for divergent PGR action are poorly understood. Here we characterised PGR activity in mouse granulosa cells using combined ChIP-seq for PGR and H3K27ac and gene expression microarray. Comparison of granulosa, uterus and oviduct PGR-dependent genes showed almost complete tissue specificity in PGR target gene profiles. In granulosa cells 82% of identified PGR-regulated genes bound PGR within 3 kb of the gene and PGR binding sites were highly enriched in proximal promoter regions in close proximity to H3K27ac-modified active chromatin. Motif analysis showed highly enriched PGR binding to the PGR response element (GnACAnnnTGTnC), but PGR also interacted significantly with other transcription factor binding motifs. In uterus PGR showed far more tendency to bind intergenic chromatin regions and low evidence of interaction with other transcription factors. This is the first genome-wide description of PGR action in granulosa cells and systematic comparison of diverse PGR action in different reproductive tissues. It clarifies finely-tuned contextual PGR-chromatin interactions with implications for more targeted reproductive medicine.

Functional coordination of three mitotic motors in Drosophila embryos.

It is well established that multiple microtubule-based motors contribute to the formation and function of the mitotic spindle, but how the activities of these motors interrelate remains unclear. Here we visualize spindle formation in living Drosophila embryos to show that spindle pole movements are directed by a temporally coordinated balance of forces generated by three mitotic motors, cytoplasmic dynein, KLP61F, and Ncd. Specifically, our findings suggest that dynein acts to move the poles apart throughout mitosis and that this activity is augmented by KLP61F after the fenestration of the nuclear envelope, a process analogous to nuclear envelope breakdown, which occurs at the onset of prometaphase. Conversely, we find that Ncd generates forces that pull the poles together between interphase and metaphase, antagonizing the activity of both dynein and KLP61F and serving as a brake for spindle assembly. During anaphase, however, Ncd appears to have no effect on spindle pole movements, suggesting that its activity is down-regulated at this time, allowing dynein and KLP61F to drive spindle elongation during anaphase B.

Inhibition of ribulose-1,5-bisphosphate carboxylase-oxygenase activities by hydroxylamine.

Hydroxylamine directly and reversibly inhibits both activities of homogeneous ribulose-1,5-bisphosphate carboxylase-oxygenase (3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 4.1.1.39) isolated from diverse sources. NH2OH is an uncompetitive inhibitor of carboxylase activity with respect to ribulose-bisphosph ate. This reagent also reacts non-enzymically with ribulosebisphosphate to deplete this substrate. Contrary to previous reports, these results indicate that hydroxylamine directly and indirectly inhibits both activities of this bifunctional enzyme.

Effect of low-density lipoprotein on the expression of high affinity Fc gamma receptors.

A substrain of the human monocyte-like cell line U937, which is a cholesterol auxotroph, was used to study the effect of cellular cholesterol depletion on the expression of the type I Fc receptor for IgG (Fc gamma RI). Measurement of Fc gamma RI expression was performed by immunofluorescence and flow cytometry using the monoclonal antibody (mAb) 32.2, which is specific for an epitope on Fc gamma RI, and monomeric IgG2a, which binds to the ligand binding site of Fc gamma RI. Incubation of these cells for 24 h in growth medium containing delipidated fetal calf serum depletes cellular cholesterol without affecting growth or viability. While incubation of U937 cells with human interferon-gamma (IFN-gamma) increased Fc gamma RI expression, cholesterol depletion after cell growth in media containing delipidated serum and IFN-gamma resulted in reduced binding of both mAb 32.2 and IgG2a. A significant decrease in the number of cell surface binding sites, as measured by mean fluorescence intensity, was observed after cholesterol depletion. Supplementation of the delipidated serum medium with pure cholesterol in an ethanol/bovine serum albumin mixture, which replenished cellular cholesterol and supported growth, failed to restore antibody binding significantly. In contrast, low-density lipoprotein (LDL) which also delivered cholesterol to the cells restored binding both in terms of the number of the reactive cells and cell surface receptor density. High-density lipoprotein (HDL3), which does not deliver cholesterol to the cells, showed results similar to those obtained with pure cholesterol. This indicates that either LDL cholesterol is better utilized for membrane synthesis than pure cholesterol or that LDL provides another component, in addition to cholesterol, which is required for expression of Fc gamma RI, but not for growth. These studies indicate a role for LDL in regulating the expression of Fc gamma RI on the cell surface.

A direct correlation between nicotinamide N-methyltransferase activity and protein levels in human liver cytosol.

Phenotypic differences in nicotinamide N-methyltransferase (NNMT, E. C. 2.1.1.1) activity may be due to a genetic polymorphism. We report the characterisation of the hepatic NNMT activity in cytosol from normal human livers, enzyme protein levels determined by Western blotting and ELISA and mRNA levels determined by SDS-PAGE/Northern blotting. Subjects with high NNMT activity had high levels of NNMT protein and NNMT mRNA levels in hepatic cytosol and the converse was true for individuals with low NNMT activity. No differences in sequences were seen when cDNAs of individuals with high and low NNMT activity were compared. Thus phenotypic differences in the general population are due to differences in steady-state mRNA levels and not because of a polymorphism in the coding region of the NNMT gene.

Intracellular Na+, K+, and C1- activities in Balanus photoreceptors.

Ion-sensitive microelectrodes were used to measure intracellular activities (aix) of Na+, K+, and C-1 in Balanus photoreceptors. Average values of aiNa, aiK, and aiCl were 28 mM, 120 mM, and 65 mM, respectively. Equilibrium potentials calculated from these average values were: Na+ +64 mV, K+ - 77 mV, and and Cl- -42 mV; ther average value of the resting potential for all cells examined was -41 mV. Long exposure to intense illumination produced measurable increases in aiNa. Classical Na+ - K+ reciprocal dilution experiments were analyzed with and without observed changes in aiK. As aoK was increased, the membrane depolarized, and aiK increased. Better agreement was found between the membrane potential and the directly determined EK than expected from the standard relation between Em and aoK. The latter produced pNa:pK estimates of the resting photoreceptor membrane that were higher than estimates based on data from the ion electrodes. Generally, Em was more negative than EK as aoK was increased. This is consistent with a significant chloride permeability in the dark-adapted photoreceptor.

The electrical response of the planarian ocellus.

The planarian ocellar potential (OP), an action potential evoked from the planarian ocellus by a light flash, was recorded with microelectrodes. OP amplitude, latency, and peak delay varied as a function of stimulus intensity and state of adaptation in a manner similar to the responses of other photoreceptors. Changes in the OP that occurred with different directions of incident light are described and attributed to screening effects of the ocellar pigment cells. The temperature coefficient (Q(10)) of OP latency was 1.5; latency decreased continuously as temperature was increased to destructive levels. The energy of activation of the rate of OP formation was calculated to approximate 10 kcal. These findings suggest dependence of OP latency on ionic diffusion and of OP formation on a biocatalytic process.