The paradox of expert judgment in rivers ecological monitoring.

A great investment has been done in the last decades in the development of numerical and qualitative assessment methods to classify the ecological quality of water bodies. Yet, in spite of all attempts to avoid subjectivity, expert judgment is still used at numerous steps of the ecological classification and is considered by some authors as indispensible for management purposes. Thus, the aim of this study is to test the hypothesis that expert judgment, when done by the adequate experts (limnologists/river ecologist) with experience in the study area (i.e., natural conditions and expected communities), could be as good as quantitative indices and measures (i.e., result in the same classification), but quicker and with lower cost. For that we compared the classifications (on 13 aspects of rivers ecosystems) attributed by two experts to 20 sites (10 each) located in their study areas, with the classifications of ecological quality based on biological indices (for invertebrates and diatoms), hydromorphology and water chemistry, calculated by an independent team. Our results show that assessments made by experts and those calculated through indices (biological quality and hydromorphology) are globally very similar (RELATE test; Rho = 0.442; p < 0.001, 999 permutations). Most differences were of one class and experts tended to attribute a better condition than indices to the best quality sites but a worse condition to the worse quality sites. A Principal Components Analysis revealed that sites to which experts attributed a moderate quality had higher nitrate concentration and pH but were well oxygenated. The sites classified as poor and bad where those with stronger modifications in their habitats (given by the higher values of HMS). The difference between experts and indices is small but still represents 15% of sites, and includes both situations: the experts or the indices lead to the need of measures (i.e., classifications below class Good). Experts' evaluations on hydromorphological conditions of the channel and margins are also significantly correlated with the quality assessments made by the field team that has no experience in the study area (Rh0 = 0.518; p = 0.001; 999 permutation), indicating geographic independence in the expert judgment. We concluded that expert judgment could be used in the determination of streams and rivers ecological quality, saving money and time and helping to redirect monitoring funds to actual implementation of restoration measures. Yet, classification' scoring methods may still be useful for a better targeting of restoration measures.

Temperature dependence of cloned mammalian and salmonid cardiac Na(+)/Ca(2+) exchanger isoforms.

The cardiac Na(+)/Ca(2+) exchanger (NCX), an important regulator of cytosolic Ca(2+) concentration in contraction and relaxation, has been shown in trout heart sarcolemmal vesicles to have high activity at 7 degrees C relative to its mammalian isoform. This unique property is likely due to differences in protein structure. In this study, outward NCX currents (I(NCX)) of the wild-type trout (NCX-TR1.0) and canine (NCX 1.1) exchangers expressed in oocytes were measured to explore the potential contributions of regulatory vs. transport mechanisms to this observation. cRNA was transcribed in vitro from both wild-type cDNA and was injected into Xenopus oocytes. I(NCX) of NCX-TR1.0 and NCX1.1 were measured after 3-4 days over a temperature range of 7-30 degrees C using the giant excised patch technique. The I(NCX) for both isoforms exhibited Na(+)-dependent inactivation and Ca(2+)-dependent positive regulation. The I(NCX) of NCX1.1 exhibited typical mammalian temperature sensitivities with Q(10) values of 2.4 and 2.6 for peak and steady-state currents, respectively. However, the I(NCX) of NCX-TR1.0 was relatively temperature insensitive with Q(10) values of 1.2 and 1.1 for peak and steady-state currents, respectively. I(NCX) current decay was fit with a single exponential, and the resultant rate constant of inactivation (lambda) was determined as a function of temperature. As expected, lambda decreased monotonically with temperature for both isoforms. Although lambda was significantly greater in NCX1.1 compared with NCX-TR1.0 at all temperatures, the effect of temperature on lambda was not different between the two isoforms. These data suggest that the disparities in I(NCX) temperature dependence between these two exchanger isoforms are unlikely due to differences in their inactivation kinetics. In addition, similar differences in temperature dependence were observed in both isoforms after alpha-chymotrypsin treatment that renders the exchanger in a deregulated state. These data suggest that the differences in I(NCX) temperature dependence between the two isoforms are not due to potential disparities in either the I(NCX) regulatory mechanisms or structural differences in the cytoplasmic loop but are likely predicated on differences within the transmembrane segments.

Inhibition of Na+/Ca2+ exchange by KB-R7943: transport mode selectivity and antiarrhythmic consequences.

The Na+/Ca2+ exchanger plays a prominent role in regulating intracellular Ca2+ levels in cardiac myocytes and can serve as both a Ca2+ influx and efflux pathway. A novel inhibitor, KB-R7943, has been reported to selectively inhibit the reverse mode (i.e., Ca2+ entry) of Na+/Ca2+ exchange transport, although many aspects of its inhibitory properties remain controversial. We evaluated the inhibitory effects of KB-R7943 on Na+/Ca2+ exchange currents using the giant excised patch-clamp technique. Membrane patches were obtained from Xenopus laevis oocytes expressing the cloned cardiac Na+/Ca2+ exchanger NCX1.1, and outward, inward, and combined inward-outward currents were studied. KB-R7943 preferentially inhibited outward (i.e., reverse) Na+/Ca2+ exchange currents. The inhibitory mechanism consists of direct effects on the transport machinery of the exchanger, with additional influences on ionic regulatory properties. Competitive interactions between KB-R7943 and the transported ions were not observed. The antiarrhythmic effects of KB-R7943 were then evaluated in an ischemia-reperfusion model of cardiac injury in Langendorff-perfused whole rabbit hearts using electrocardiography and measurements of left ventricular pressure. When 3 microM KB-R7943 was applied for 10 min before a 30-min global ischemic period, ventricular arrhythmias (tachycardia and fibrillation) associated with both ischemia and reperfusion were almost completely suppressed. The observed electrophysiological profile of KB-R7943 and its protective effects on ischemia-reperfusion-induced ventricular arrhythmias support the notion of a prominent role of Ca2+ entry via reverse Na+/Ca2+ exchange in this process.

Ionic regulatory properties of brain and kidney splice variants of the NCX1 Na(+)-Ca(2+) exchanger.

Ion transport and regulation of Na(+)-Ca(2+) exchange were examined for two alternatively spliced isoforms of the canine cardiac Na(+)-Ca(2+) exchanger, NCX1.1, to assess the role(s) of the mutually exclusive A and B exons. The exchangers examined, NCX1.3 and NCX1.4, are commonly referred to as the kidney and brain splice variants and differ only in the expression of the BD or AD exons, respectively. Outward Na(+)-Ca(2+) exchange activity was assessed in giant, excised membrane patches from Xenopus laevis oocytes expressing the cloned exchangers, and the characteristics of Na(+)(i)- (i.e., I(1)) and Ca(2+)(i)- (i.e., I(2)) dependent regulation of exchange currents were examined using a variety of experimental protocols. No remarkable differences were observed in the current-voltage relationships of NCX1.3 and NCX1.4, whereas these isoforms differed appreciably in terms of their I(1) and I(2) regulatory properties. Sodium-dependent inactivation of NCX1.3 was considerably more pronounced than that of NCX1.4 and resulted in nearly complete inhibition of steady state currents. This novel feature could be abolished by proteolysis with alpha-chymotrypsin. It appears that expression of the B exon in NCX1.3 imparts a substantially more stable I(1) inactive state of the exchanger than does the A exon of NCX1.4. With respect to I(2) regulation, significant differences were also found between NCX1.3 and NCX1.4. While both exchangers were stimulated by low concentrations of regulatory Ca(2+)(i), NCX1.3 showed a prominent decrease at higher concentrations (>1 microM). This does not appear to be due solely to competition between Ca(2+)(i) and Na(+)(i) at the transport site, as the Ca(2+)(i) affinities of inward currents were nearly identical between the two exchangers. Furthermore, regulatory Ca(2+)(i) had only modest effects on Na(+)(i)-dependent inactivation of NCX1.3, whereas I(1) inactivation of NCX1.4 could be completely eliminated by Ca(2+)(i). Our results establish an important role for the mutually exclusive A and B exons of NCX1 in modulating the characteristics of ionic regulation and provide insight into how alternative splicing tailors the regulatory properties of Na(+)-Ca(2+) exchange to fulfill tissue-specific requirements of Ca(2+) homeostasis.