Leukocytospermia and sperm preparation - a flow cytometric study

Reprod Biol Endocrinol. 2009 Nov 19;7:12

Membrane potential and Ca2+ concentration dependence on pressure and vasoactive agents in arterial smooth muscle: A model

Arterial smooth muscle (SM) cells respond autonomously to changes in intravascular pressure, adjusting tension to maintain vessel diameter. The values of membrane potential (V_m) and sarcoplasmic Ca^2+ concentration (Ca_in) within minutes of a change in pressure are the results of two opposing pathways, both of which use Ca^2+ as a signal. This works because the two Ca^2+-signaling pathways are confined to distinct microdomains in which the Ca^2+ concentrations needed to activate key channels are transiently higher than Cain. A mathematical model of an isolated arterial SM cell is presented that incorporates the two types of microdomains. The first type consists of junctions between cisternae of the peripheral sarcoplasmic reticulum (SR), containing ryanodine receptors (RyRs), and the sarcolemma, containing voltage- and Ca^2+-activated K^+ (BK) channels. These junctional microdomains promote hyperpolarization, reduced Cain, and relaxation. The second type is postulated to form around stretch-activated nonspecific cation channels and neighboring Ca^2+-activated Cl^− channels, and promotes the opposite (depolarization, increased Ca_in, and contraction). The model includes three additional compartments: the sarcoplasm, the central SR lumen, and the peripheral SR lumen. It incorporates 37 protein components. In addition to pressure, the model accommodates inputs of α- and β-adrenergic agonists, ATP, 11,12-epoxyeicosatrienoic acid, and nitric oxide (NO). The parameters of the equations were adjusted to obtain a close fit to reported Vm and Ca_in as functions of pressure, which have been determined in cerebral arteries. The simulations were insensitive to ±10% changes in most of the parameters. The model also simulated the effects of inhibiting RyR, BK, or voltage-activated Ca^2+ channels on V_m and Ca_in. Deletion of BK β1 subunits is known to increase arterial–SM tension. In the model, deletion of β1 raised Ca_in at all pressures, and these increases were reversed by NO

Hydrological modelling of water allocation, ecosystem services and poverty alleviation in the Pongola floodplain, South Africa

The Pongola River Ecosystem Services for Poverty Alleviation (PRESPA) project quantified the economic benefits accuring to different livelihood sectors from the water resources of the Pongola floodplain, South Africa. The floodplain carries a diverse economy and ecology which is supported by flood events that once occured naturally but are now regulated by an upstream dam. PRESPA modelled the eco-hydrology which underpins various ecosystem services to determine how this might be managed to alleviate poverty. A model was used to quantify the economic value of the available water, especially the value accruing to the poor. This model linked to three development scenarios to explore trade-offs and outcomes of (1) a status quo, 'unstructured' economy; (2) a structured diverse economy; and (3) a structured 'single sector' agricultural economy. This model gives decision makers ameasure of where water is best used in terms of poverty alleviation and enables them to examine future economic and ecosystem trajectories. In summary, poor households on the floodplain currently have a diversity of income and food sources, making them less vulnerable to economic and climatic shocks, while there is a trend towards intensive agriculture which may deliver higher returns but with greater costs and increased vulnerability