Environmental regulation can arise under minimal assumptions.

Models that demonstrate environmental regulation as a consequence of organism and environment coupling all require a number of core assumptions. Many previous models, such as Daisyworld, require that certain environment-altering traits have a selective advantage when those traits also contribute towards global regulation. We present a model that results in the regulation of a global environmental resource through niche construction without employing this and other common assumptions. There is no predetermined environmental optimum towards which regulation should proceed assumed or coded into the model. Nevertheless, polymorphic stable states that resist perturbation emerge from the simulated co-evolution of organisms and environment. In any single simulation a series of different stable states are realised, punctuated by rapid transitions. Regulation is achieved through two main subpopulations that are adapted to slightly different resource values, which force the environmental resource in opposing directions. This maintains the resource within a comparatively narrow band over a wide range of external perturbations. Population driven oscillations in the resource appear to be instrumental in protecting the regulation against mutations that would otherwise destroy it. Sensitivity analysis shows that the regulation is robust to mutation and to a wide range of parameter settings. Given the minimal assumptions employed, the results could reveal a mechanism capable of environmental regulation through the by-products of organisms.

PerFlexMEA: a thin microporous microelectrode array for in vitro cardiac electrophysiological studies on hetero-cellular bilayers with controlled gap junction communication.

The new microelectrode array device presented is called PerFlexMEA and it enables controlled coupling between myocytes and nonmyocytes used in cardiovascular conduction studies. The device consists of an 8 µm thin parylene microporous membrane with a 4 × 5 microelectrode array patterned on one side. Myocytes and nonmyocytes can be plated on either side of the parylene membrane to create a tissue bilayer. The 3-3.5 µm diameter pores allow inter-layer dye and electrical coupling without transmembrane cell migration. Cell migration was found to vary with cell-type and micropore diameter. Pore density can be varied based on desired coupling ratio. The flexible parylene membrane is packaged between two rigid thermoplastic layers, such that the microelectrode array region is exposed, while the rest of the device remains insulated. The packaged PerFlexMEA fits in a 60 mm culture dish. Recording experiments are performed by simply plugging it into a commercially available multielectrode amplifier system. Recorded signals were processed and analysed using scripts generated in MATLAB. Our experimental results provide evidence of the reliability of this device, as conduction velocity was observed to decrease after inducing lateral hetero-cellular controlled coupling between myocytes and HeLa cells expressing connexin 43.

Body elemental composition, with particular reference to total and exchangeable sodium and potassium and total chlorine, in untreated and treated primary hyperaldosteronism.

The whole body content of sodium, potassium, chlorine, calcium, phosphorus and nitrogen was measured by neutron activation analysis in 13 patients with untreated primary hyperaldosteronism (Conn's syndrome; aldosterone-secreting adenoma). Concurrently, exchangeable sodium and potassium were estimated by isotope dilution. Results were compared with values in the same patients during treatment with potassium-conserving diuretics and again after removal of the adenoma; and also with those in a series of 30 patients having untreated essential hypertension. Both total body and exchangeable sodium were high in Conn's syndrome before treatment and were reduced by spironolactone or amiloride and by subsequent surgery. There was no evidence of alteration in the proportion of non-exchangeable sodium in this disease, in contrast to earlier reports. Total body and exchangeable potassium were low in untreated Conn's syndrome and increased to normal after therapy: the proportion of non-exchangeable potassium was similar before and after treatment, and also similar to that in essential hypertension. Total body chlorine was increased before treatment in Conn's syndrome and returned to normal with therapy; body calcium, phosphorus and nitrogen were normal throughout.

Whole-body elemental composition in patients with renal failure and after transplantation studied using total-body neutron-activation analysis.

Whole body elemental composition in seventy-five patients with either renal failure or a kidney transplant was measured by neutron-activation analysis and whole-body counting. Comparison was made with expected normal values and with a control group; between undialysed, dialysed and transplanted patients; and between those receiving dialysis treatment for various periods. A frequent finding was low body calcium, reflecting the prevalence of renal osteodystrophy. Sodium and chlorine were increased in undialysed patients, a consequence of their renal disease. Patients with transplanted kidneys had reduced amounts of most elements, indicating decreased lean body mass, but increased body weight, probably due to excess fat.

Whole body elemental composition in patients with essential hypertension.

The whole body content of sodium, chlorine and potassium has been measured in 30 patients with essential hypertension, using the techniques of in vivo neutron activation analysis and whole body counting. Total exchangeable sodium and potassium were also measured, and found to be well correlated with the total body amounts of these elements. Comparable measurements on normotensive subjects could not be obtained, but results for both elements were similar to those expected on the basis of published values for healthy normal body composition. Similarly, no abnormality was found in the average body content of the other major elements (chlorine, calcium, phosphorus and nitrogen). We therefore have no evidence that essential hypertension is associated with any abnormality in the mean body content of these elements. However, there was some evidence of a relationship between body sodium and blood pressure in this study group.