Ian C. Forster

Feeding aquaculture in an era of finite resources

Aquacultures pressure on forage fisheries remains hotly contested. This article reviews trends in fishmeal and fish oil use in industrial aquafeeds, showing reduced inclusion rates but greater total use associated with increased aquaculture production and demand for fish high in long-chain omega-3 oils. The ratio of wild fisheries inputs to farmed fish output has fallen to 0.63 for the aquaculture sector as a whole but remains as high as 5.0 for Atlantic salmon. Various plant- and animal-based alternatives are now used or available for industrial aquafeeds, depending on relative prices and consumer acceptance, and the outlook for single-cell organisms to replace fish oil is promising. With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it.

The sodium phosphate cotransporter family SLC34

This review summarizes the characteristics of the solute carrier family SLC34 that is represented by the type ll Na/Pi-cotransporters NaPi-lla (SLC34A1), NaPi-llb (SLC34A2) and NaPi-llc (SLC34A3). Other Na/Pi-cotransporters are described within the SLC17 and SLC20 families. Type ll Na/Pi-cotransporters are expressed in several tissues and play a major role in the homeostasis of inorganic phosphate. In kidney and small intestine, type ll Na/Pi-cotransporters are located at the apical sites of epithelial cells and represent the rate limiting steps for transepithelial movement of phosphate. Physiological and pathophysiological regulation of renal and small intestinal epithelial transport of phosphate occurs through alterations in the abundance of type ll Na/Pi-cotransporters.

Mutations in SLC20A2 link familial idiopathic basal ganglia calcification with phosphate homeostasis

Familial idiopathic basal ganglia calcification (IBGC) is a genetic condition with a wide spectrum of neuropsychiatric symptoms, including parkinsonism and dementia. Here, we identified mutations in SLC20A2, encoding the type III sodium-dependent phosphate transporter 2 (PiT2), in IBGC-affected families of varied ancestry, and we observed significantly impaired phosphate transport activity for all assayed PiT2 mutants in Xenopus laevis oocytes. Our results implicate altered phosphate homeostasis in the etiology of IBGC.

Potential for dietary phytase to improve the nutritive value of canola protein concentrate and decrease phosphorus output in rainbow trout (Oncorhynchus mykiss) held in 11°C fresh water

This study assessed the potential for using dietary phytase to improve the nutritive value of canola protein concentrate (CPC) for rainbow trout, and to concomitantly minimize phosphorus discharge into the environment. Eight diets were prepared. LT-anchovy meal (AM) provided 89% of the protein in the basal diet, whereas in the remaining diets, 59% of the protein originated from CPC by replacement of AM protein. Four CPC diets were supplemented with phytase (Natuphos®) at levels of either 0, 500, 1500 or 4500 phytase units (FTU)/kg diet together with 4505 mg/kg phosphorus. Two CPC diets contained 1500 FTU/kg and either 0 or 2253 mg/kg of supplemental phosphorus. The seventh CPC diet contained no phytase or supplemental phosphorus. A commercial trout feed served as an industry control. All diets were fed to triplicate groups of rainbow trout (initial weight, 17.9 g) to satiation daily for 84 days. Mean water temperature was 11.0°C. The level of phytic acid degradation and the apparent availability of dietary phosphorus were ascertained for all groups. Fish fed the CPC diets, regardless of their phytase and phosphorus levels, exhibited growth rates, feed efficiencies and protein utilization comparable to those of control fish. There was, however, a clear positive dose-response of phytase on dietary phytate digestibility and phosphorus availability was improved significantly by the highest level of phytase. We conclude that dietary phytase has potential to improve the nutritive quality of CPC for rainbow trout and the availability of phytate phosphorus.

Lysine requirement of juvenile Japanese flounder Paralichthys olivaceus and juvenile red sea bream Pagrus major

Abstract The lysine requirement of juvenile Japanese flounder (3.0 g initial weight) and red sea bream (1.7 g initial weight) was estimated by feeding six semi-moist diets (45–48% crude protein on dry basis) containing graded levels of lysine hydrogen chloride in replacement of sodium glutamate. Most of the amino acids in the diets were provided by zein, fish meal and gelatin. In addition, free amino acids were added to ensure that the requirements for the essential amino acids, other than lysine, were met. Specific growth rate, feed efficiency, and nitrogen retention data were analyzed by non-linear regression using the broken-line model to obtain the lysine requirement estimates for Japanese flounder of 3.3, 4.2 and 4.6% of dietary protein, respectively, and 3.6, 4.3, and 4.4% of dietary protein for red sea bream. Estimates of the requirements for the other essential amino acids were made based on A / E ratios of the whole-body amino acid profile.

Regulation of phosphate transport in proximal tubules

Homeostasis of inorganic phosphate (Pi) is primarily an affair of the kidneys. Reabsorption of the bulk of filtered Pi occurs along the renal proximal tubule and is initiated by apically localized Na+-dependent Pi cotransporters. Tubular Pi reabsorption and therefore renal excretion of Pi is controlled by a number of hormones, including phosphatonins, and metabolic factors. In most cases, regulation of Pi reabsorption is achieved by changing the apical abundance of Na+/Pi cotransporters. The regulatory mechanisms involve various signaling pathways and a number of proteins that interact with Na+/Pi cotransporters.

The Na+-Pi cotransporter PiT-2 (SLC20A2) is expressed in the apical membrane of rat renal proximal tubules and regulated by dietary Pi

The principal mediators of renal phosphate (P(i)) reabsorption are the SLC34 family proteins NaPi-IIa and NaPi-IIc, localized to the proximal tubule (PT) apical membrane. Their abundance is regulated by circulatory factors and dietary P(i). Although their physiological importance has been confirmed in knockout animal studies, significant P(i) reabsorptive capacity remains, which suggests the involvement of other secondary-active P(i) transporters along the nephron. Here we show that a member of the SLC20 gene family (PiT-2) is localized to the brush-border membrane (BBM) of the PT epithelia and that its abundance, confirmed by Western blot and immunohistochemistry of rat kidney slices, is regulated by dietary P(i). In rats treated chronically on a high-P(i) (1.2%) diet, there was a marked decrease in the apparent abundance of PiT-2 protein in kidney slices compared with those from rats kept on a chronic low-P(i) (0.1%) diet. In Western blots of BBM from rats that were switched from a chronic low- to high-P(i) diet, NaPi-IIa showed rapid downregulation after 2 h; PiT-2 was also significantly downregulated at 24 h and NaPi-IIc after 48 h. For the converse dietary regime, NaPi-IIa showed adaptation within 8 h, whereas PiT-2 and NaPi-IIc showed a slower adaptive trend. Our findings suggest that PiT-2, until now considered as a ubiquitously expressed P(i) housekeeping transporter, is a novel mediator of P(i) reabsorption in the PT under conditions of acute P(i) deprivation, but with a different adaptive time course from NaPi-IIa and NaPi-IIc.

Nucleotide recognition by the cytoplasmic domain of the human chloride transporter ClC-5

The ubiquitous CBS domains, which are found as part of cytoplasmic domains in the ClC family of chloride channels and transporters, have previously been identified as building blocks for regulatory nucleotide-binding sites. Here we report the structures of the cytoplasmic domain of the human transporter ClC-5 in complex with ATP and ADP. The nucleotides bind to a specific site in the protein. As determined by equilibrium dialysis, the affinities for ATP, ADP and AMP are in the high micromolar range. Point mutations that interfere with nucleotide binding change the transport behavior of a ClC-5 mutant expressed in Xenopus laevis oocytes. Our results establish the structural and energetic basis for the interaction of ClC-5 with nucleotides and provide a framework for future investigations.

A multiple electrode cochlear implant

The University of Melbourne Departments of Otolaryngology and Electrical Engineering (UMDOLEE) receiving and stimulating component of a multiple-electrode cochlear implant hearing prosthesis produces constant stimulation. It has a stimulating pulse shape that minimizes the production of toxic substances and loss of metal from the electrodes, and this is achieved with a biphasic rectangular waveform where the first phase is negative with respect to ground. The duration of each stimulus phase in 180 msec, which is long enough to allow low levels of current stimulation, and short enough to permit rates of 1000 pulses/second to be achieved. In order to be consistent with our present understanding of the perception of pitch, the device permits the independent stimulation of a number of electrodes. Furthermore, to electrically isolate the stimulus to small areas, there is the capacity to vary the current and set the threshold independently at individual electrodes. The phase and amplitude of the pulses to neighbouring electrodes with also be varied to assist in localizing the current flow. The pattern to stimulation to individual or groups of electrodes can also be altered to enable studies to be carried out to determine ways of conveying frequency and intensity information over a more normal dynamic range.

Erythropoietin modulates intracellular calcium in a human neuroblastoma cell line

1 Recent investigations have shown that the glycoprotein erythropoietin (Epo) and its specific receptor (EpoR) are present in the mammalian brain including human, monkey and mouse. These findings suggest a local action of Epo in the nervous system. The aim of this study was to elucidate a possible functional interaction of Epo with neuronal cells. 2 To examine the influence of externally applied Epo on Ca2+ homeostasis the human neuroblastoma cell line SK‐N‐MC was chosen as a suitable in vitro model for undifferentiated neuronal cells. 3 Expression of the EpoR in SK‐N‐MC cells was detected by reverse transcription‐PCR, Western blot and immunofluorescence analysis. 4 Patch‐clamp studies of SK‐N‐MC cells confirmed the expression of T‐type Ca2+ channels, whose peak macroscopic current was increased by the addition of recombinant human Epo (rhEpo) to the bathing medium. 5 Confocal laser scanning microscopy analysis of SK‐N‐MC cells confirmed a transient increase in intracellular free [Ca2+] in response to externally applied rhEpo. 6 The transient response to Epo was dependent on external Ca2+ and remained even after depletion of internal Ca2+ stores by caffeine or thapsigargin. However, after depletion the response to Epo was absent when cells were superfused with the T‐type Ca2+ channel blocker flunarizine. 7 This study demonstrates that Epo can interact with neuronal cells by affecting Ca2+ homeostasis through an increase in Ca2+ influx via plasma membrane T‐type voltage‐dependent Ca2+ channels.