Factors controlling hypolimnetic ammonia accumulation in a lake

Abstract : The factors controlling the degree of hypolimnetic ammonia accumulation in Lake Onogawa are discussed based on periodic observations since 1993. The standing stock of ammonia in the bottom 9m of the water column was a good measurement for determining the extent of the hypolimnetic ammonia accumulation. It varied threefold from 144mmolm~-2 in 1998 to 429mmolm~-2 in 1996. The correlation between the annual maxima of the ammonia standing stocks and the annual maxima of the thickness of anoxic layers was significant at P = 0.01. This fact suggests that the degree of development of the anoxic layer is the primary factor controlling the extent of hypolimnetic ammonia accumulation. Sporadic local heavy rainfalls in 1998 perturbed the water column, and the formation of the anoxic layer was postponed more than one month, resulting in a lower level of hypolimnetic ammonia accumulation in 1998. A thick mineral deposit apparently formed during the local heavy rainfall and seemed to enclose the freshly deposited organic matter, which might be an effective source material of the hypolimnetic ammonia, and resulted in a low level of ammonia accumulation in 1999. By 2000, the lake seems to have recovered from the perturbation, suggesting that the major part of the hypolimnetic ammonia is derived from fresh organic matter deposited within a year.　Key words : Lake Onogawa・Anoxic layer・Lake perturbation・Ammonia sourc

Bubble Liposomes and Ultrasound Exposure Improve Localized Morpholino Oligomer Delivery into the Skeletal Muscles of Dystrophic <i>mdx</i> Mice

Duchenne muscular dystrophy (DMD) is a genetic disorder that is caused by mutations in the DMD gene that lead to an absence of functional protein. The <i>mdx</i> dystrophic mouse contains a nonsense mutation in exon 23 of the dystrophin gene; a phosphorodiamidate morpholino oligomer (PMO) designed to skip this mutated exon in the mRNA induces dystrophin expression. However, an efficient PMO delivery method is needed to improve treatment strategies for DMD. We previously developed polyethylene glycol (PEG)-modified liposomes (Bubble liposomes) that entrap ultrasound contrast gas and demonstrated that the combination of Bubble liposomes with ultrasound exposure is an effective gene delivery tool <i>in vitro</i> and <i>in vivo</i>. In this study, to evaluate the ability of Bubble liposomes as a PMO delivery tool, we tested the potency of the Bubble liposomes combined with ultrasound exposure to boost the delivery of PMO and increase the skipping of the mutated exon in the <i>mdx</i> mouse. The results indicated that the combination of Bubble liposomes and ultrasound exposure increased the uptake of the PMO targeting a nonsense mutation in exon 23 of the dystrophin gene and consequently increased the PMO-mediated exon-skipping efficiency compared with PMO injection alone, leading to significantly enhanced dystrophin expression. This increased efficiency indicated the potential of the combination of Bubble liposomes with ultrasound exposure to enhance PMO delivery for treating DMD. Thus, this ultrasound-mediated Bubble liposome technique may provide an effective, noninvasive, nonviral method for PMO therapy for DMD muscle as well as for other muscular dystrophies