Planktonic predators and copepod abundance near the Dutch coast

Hypotheses that planktonic predators are responsible for thespring-summer decrease in copepod abundance and that the dominantpredator, Pleurobrachia pileus, is associated with high concentrationsof copepods were investigated at a station near the Dutch coast.Neither hypothesis was supported. Predators and copepods weresampled together with a 156 L ‘water box’ from lateApril through early July, including the season of P.pileus abundance.Using predators and copepods from the same box samples, hencefrom the same water parcel, feeding rates on copepod naupliiand copepodites + adults were measured onboard ship. Less than6% of the copepods, the sensitivity of the method, were removedper day. In additional shipboard feeding experiments net-caughtP.pileus were added to ambient copepod densities. By combiningwater volume cleared of copepods with ambient P.pileus densityin the sea, the predicted impact was 0–1.6% of copepodseaten per day from late April to early July. The hypothesisthat P.pileus associates with copepod concentrations was testedby comparing abundances of both groups from the same box samples.The correlations were not significant for any sample series.The ways measurement methods have restricted progress in understandingthe predatory impact of Pleurobrachia sp. are also considered.     

Liposomes and biotherapeutics

Application of liposomes as delivery system for biotherapeutic peptides and proteins may offer important therapeutic advantages over existing delivery methods. Several approaches towards achieving improved delivery of biotherapeutics with liposomes are outlined. Although the literature on this topic is sporadic and frequently incomplete, enough of a research foundation exists to justify the conclusion that liposomes can play an important role in the formulation and delivery of biotherapeutics. However, it will be necessary to understand more fully the mechanisms of action before optimum liposomal dosage forms can be designed.     

Regulation of GPCR signaling in Hypertension

Hypertension represents a complex, multifactorial disease and contributes to the major causes of morbidity and mortality in industrialized countries: ischemic and hypertensive heart disease, stroke, peripheral atherosclerosis and renal failure. Current pharmacological therapy of essential hypertension focuses on the regulation of vascular resistance by inhibition of hormones such as catecholamines and angiotensin II, blocking them from receptor activation. Interaction of G-protein coupled receptor kinases (GRKs) and regulator of G-protein signaling (RGS) proteins with activated G-protein coupled receptors (GPCRs) effect the phosphorylation state of the receptor leading to desensitization and can profoundly impair signaling. Defects in GPCR regulation via these modulators have severe consequences affecting GPCR-stimulated biological responses in pathological situations such as hypertension, since they fine-tune and balance the major transmitters of vessel constriction versus dilatation, thus representing valuable new targets for anti-hypertensive therapeutic strategies. Elevated levels of GRKs are associated with human hypertensive disease and are relevant modulators of blood pressure in animal models of hypertension. This implies therapeutic perspective in a disease that has a prevalence of 65 million in the United States while being directly correlated with occurrence of major adverse cardiac and vascular events. Therefore, therapeutic approaches using the inhibition of GRKs to regulate GPCRs are intriguing novel targets for treatment of hypertension and heart failure.     

The mollusc fauna along a depth transect in the Faroe Shetland Channel: Is there a relationship with internal waves?

From boxcore and dredge samples taken along a depth transect across the Faroe Shetland Channel (FSC) in 1997 and 1999, molluscs were sorted and identified. On the basis of their numerical abundance, the stations could be clustered into three groups, reflecting the depth extension of the main water masses in the FSC. Between 400 and 500 m depth, both the number of taxa per sample and the number of specimens, were highest. Bivalves were mainly caught by the boxcorer and the dredge was best suited to collect the epifaunal gastropods. According to the literature, at mid-slope depths, resuspension is increased by the action of internal waves, which leads to the development of intermediate nepheloid layers. This increased concentration of suspended matter may serve as a food source of low quality. Likewise the low amounts of suspended matter with a relatively high quality of particulate organic matter, such as from ∼400 and ∼700 m may act similarly and explain the relative high abundance of filter feeders at these depths. However, in the various multivariate analyses we could not distinguish the fauna from these depths from that collected from other sites. We observed, however, a pattern in the depth distribution of feeding guilds across the slope of the FSC. Deposit feeders demonstrated a trend of decreasing numbers with depth. Filter-feeding taxa were found to have peaks at depths of approximately 350 m, between 500 and 600 m and between 700 and 800 m. This observation supports the idea that the fauna at the deep sites reflects the locally high cross-slope currents and the subsequent increased amounts or availability of food with a better quality, which seems to be related to resuspension events.     

Accuracy of circadian entrainment under fluctuating light conditions: contributions of phase and period responses.

The accuracy with which a circadian pacemaker can entrain to an environmental 24-h zeitgeber signal depends on (a) characteristics of the entraining signal and (b) response characteristics and intrinsic stability of the pacemaker itself. Position of the sun, weather conditions, shades, and behavioral variations (eye closure, burrowing) all modulate the light signal reaching the pacemaker. A simple model of a circadian pacemaker allows researchers to explore the impact of these factors on pacemaker accuracy. Accuracy is operationally defined as the reciprocal value of the day-to-day standard deviation of the clock times at which a reference phase (0) is reached. For the purpose of this exploration, the authors used a model pacemaker characterized solely by its momentary phase and momentary velocity. The average velocity determines the time needed to complete one pacemaker cycle and, therefore, is inversely proportional to pacemaker period. The model pacemaker responds to light by shifting phase and/or changing its velocity. The authors assumed further that phase and velocity show small random fluctuations and that the velocity is subject to aftereffects. Aftereffects were incorporated mathematically in a term allowing period to contract exponentially to a stable steady-state value, with a time constant of 69 d in the absence of light. The simulations demonstrate that a pacemaker reaches highest accuracy when it responds to light by simultaneous phase shifts and changes of its velocity. Phase delays need to coincide with slowing down and advances with speeding up; otherwise, no synchronization to the zeitgeber occurs. At maximal accuracy, the changes in velocity are such that the average period of the pacemaker under entrained conditions equals 24 h. The results suggest that during entrainment, the pacemaker adjusts its period to 24 h, after which daily phase shifts to compensate for differences between the periods of the zeitgeber and the clock are no longer necessary. On average, phase shifts compensate for maladjustments of phase and velocity changes compensate for maladjustments of period.