Rapid regulation of electrolyte absorption in sweat duct

Even though the same Cl channel (CFTR) is common to certain fluid transport functions that are oppositely directed, i.e., secretion and absorption, only fluid secretion has clearly been shown to be acutely regulated. It is now clear that fluid secretion activated by -adrenergic stimulation is controlled by cAMP-mediated opening and closing of CFTR-Cl channels. Since the conductance of the human sweat duct is almost wholly due to CFTR-Cl conductance (CFTR-G_Cl), we sought to determine whether salt absorption via CFTR-Cl channels could also be subject to acute regulation in this purely absorptive epithelium. After -toxin permeabilization, we found that addition of cAMP resulted in a large increase in Cl diffusion potentials across the apical membrane and a more than twofold increase in the average membrane conductance. Since the cAMP effects were dependent on Cl alone, not on Na, and since apical Cl conductance appears to be almost exclusively comprised of CFTR-G_Cl, we surmise that this form of electrolyte absorption like secretion is also subject to acute control through CFTR-G_Cl. Acute regulation of absorption involves both activation by phosphorylation (PKA) and inactivation by dephosphorylation (unknown endogenous phosphatase) of CFTR. Phosphorylation of CFTR was shown by the facts that CFTR-G_Cl could be activated by cAMP and inhibited by the kinase antagonist staurosporine, or by removal of either substrate ATP or Mg²⁺ cofactor. Inactivation of CFTR-G_Cl by endogenous phosphatase(s) was indicated by a spontaneous but reversible loss of CFTR-G_Cl upon removal of cAMP. Such loss of CFTR-G_Cl activity could be prevented either by application of phosphatase inhibitors or by using phosphatase-resistant ATP--S as substrate to phosphorylate CFTR. We surmise that absorptive function is subject to rapid regulation which can be switched on and off acutely by a control system that is common to both absorptive and secretory processes and that this control is crucial to switching between conductive and nonconductive transport mechanisms during salt absorption.The authors are grateful to Mr. Kirk Taylor for expert technical assistance, and to numerous volunteer human subjects for participating in the experiments with informed consent. Supported by grants from the National Institutes of Health, DK-41329-04 and the National Cystic Fibrosis Foundation, Z 439.     

Volume regulation by flounder red blood cells in anisotonic media

The nucleated high K, low Na red blood cells of the winter flounder demonstrated a volume regulatory response subsequent to osmotic swelling or shrinkage. During volume regulation the net water flow was secondary to net inorganic cation flux. Volume regulation the net water flow was secondary to net inorganic cation flux. Volume regulation after osmotic swelling is referred to as regulatory volume decrease (RVD) and was characterized by net K and water loss. Since the electrochemical gradient for K is directed out of the cell there is no need to invoke active processes to explain RVD. When osmotically shrunken, the flounder erythrocyte demonstrated a regulatory volume increase (RVI) back toward control cell volume. The water movements characteristic of RVI were a consequence of net cellular NaCl and KCl uptake with Na accounting for 75 percent of the increase in intracellular cation content. Since the Na electrochemical gradient is directed into the cell, net Na uptake was the result of Na flux via dissipative pathways. The addition of 10(-4)M ouabain to suspensions of flounder erythrocytes was without effect upon net water movements during volume regulation. The presence of ouabain did however lead to a decreased ration of intracellular K:Na. Analysis of net Na and K fluxes in the presence and absence of ouabain led to the conclusion that Na and K fluxes via both conservative and dissipative pathways are increased in response to osmotic swelling or shrinkage. In addition, the Na and K flux rate through both pump and leak pathways decreased in a parallel fashion as cell volume was regulated. Taken as a whole, the Na and K movements through the flounder erythrocyte membrane demonstrated a functional dependence during volume regulation.     

Increased high‐latitude photosynthetic carbon gain offset by respiration carbon loss during an anomalous warm winter to spring transition

Arctic and boreal ecosystems play an important role in the global carbon (C) budget, and whether they act as a future net C sink or source depends on climate and environmental change. Here, we used complementary in situ measurements, model simulations, and satellite observations to investigate the net carbon dioxide (CO₂) seasonal cycle and its climatic and environmental controls across Alaska and northwestern Canada during the anomalously warm winter to spring conditions of 2015 and 2016 (relative to 2010–2014). In the warm spring, we found that photosynthesis was enhanced more than respiration, leading to greater CO₂ uptake. However, photosynthetic enhancement from spring warming was partially offset by greater ecosystem respiration during the preceding anomalously warm winter, resulting in nearly neutral effects on the annual net CO₂ balance. Eddy covariance CO₂ flux measurements showed that air temperature has a primary influence on net CO₂ exchange in winter and spring, while soil moisture has a primary control on net CO₂ exchange in the fall. The net CO₂ exchange was generally more moisture limited in the boreal region than in the Arctic tundra. Our analysis indicates complex seasonal interactions of underlying C cycle processes in response to changing climate and hydrology that may not manifest in changes in net annual CO₂ exchange. Therefore, a better understanding of the seasonal response of C cycle processes may provide important insights for predicting future carbon–climate feedbacks and their consequences on atmospheric CO₂ dynamics in the northern high latitudes.     

Biodeterioration of Mayan buildings at uxmal and tulum,Mexico

Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation.     

Evidence for contemporary and historical gene flow between guppy populations in different watersheds,with a test for associations with adaptive traits

In dendritic river systems, gene flow is expected to occur primarily within watersheds. Yet, rare cross‐watershed transfers can also occur, whether mediated by (often historical) geological events or (often contemporary) human activities. We explored these events and their potential evolutionary consequences by analyzing patterns of neutral genetic variation (microsatellites) and adaptive phenotypic variation (male color) in wild guppies (Poecilia reticulata) distributed across two watersheds in northern Trinidad. We found the expected signatures of within‐watershed gene flow; yet we also inferred at least two instances of cross‐watershed gene flow—one in the upstream reaches and one further downstream. The upstream cross‐watershed event appears to be very recent (41 ± 13 years), suggesting dispersal via recent flooding or undocumented human‐mediated transport. The downstream cross‐watershed event appears to be considerably older (577 ± 265 years), suggesting a role for rare geological or climatological events. Alongside these strong signatures of both contemporary and historical gene flow, we found little evidence of impacts on presumably adaptive phenotypic differentiation, except perhaps in the one instance of very recent cross‐watershed gene flow. Selection in this system seems to overpower gene flow—at least on the spatiotemporal scales investigated here.