The human dimensions of global environmental change: Ecosystem services, resilience, and governance

Global environmental change affects all societies and their environments at various spatial and temporal scales. The linking of natural ecosystems to social ones is of central importance for the analysis, mitigation of and adaptation to any action or issue related to sustainability and global change. When examining the human dimensions of environmental change, the study of ecosystem services illustrates the strong interlinkages existing between both socio-ecological systems and global change. Ecosystem services are inextricably linked to human well-being and play a central role in sustainable adaptation strategies. Environmental impact of global change can both add to social vulnerability and change resilience by altering the supply of ecosystem services and the trade-offs which can occur. It is when examining such phenomena that the importance and abilities of governance systems to shape change and responses are seen

Active Potassium Transport Across Guinea-Pig Distal Colon: Action of Secretagogues

1. Adrenaline (5 microM) stimulated a K+ secretory current by 2-2 microequiv h-\u27 cm2 in isolated guinea-pig distal colonic epithelium. This secretory activity was inhibited entirely by addition of the loop diuretic bumetanide to the serosal solution. On-going K+ uptake via the absorptive pathway was unaltered by these changes. 2. Prostaglandin E2 (PGE2, 2 microM) stimulated electrogenic K+ secretion and Cl- secretion by 3 0 and 3-6 ,microequiv h- cmM2, respectively. Serosal addition of bumetanide completely inhibited this K+ secretion but blocked only -70% of Cl- secretion. The bumetanide-insensitive Cl- secretory current was dependent on the presence of Cl- and HC03- in the bathing solutions. 3. Stimulation of electrogenic K+ secretion by PGE2 occurred with a half-maximal concentration of 4 nm, an affinity -300 times higher than that for stimulation of Cl-secretion by PGE2. 4. Forskolin (10 microM) stimulated Cl- secretion by 4-9 microequiv h-\u27 cm2. The apparent K+ secretory rate was increased by only 1-5 microequiv h-1 cm2. A bumetanide-insensitive short-circuit current (Isc) was apparent and of the same size as that stimulated by PGE2. 5. Addition of the Ca2+ ionophore A23187 (10 microM), in the presence of indomethacin (1 microM) to reduce prostaglandin production, inhibited the K+ absorptive pathway by 40% and concurrently stimulated a small rate of electrogenic K+ secretion. 6. Active K+ absorption was inhibited by the addition of ouabain, omeprazole or SCH28080 to the mucosal solution. Both omeprazole and SCH28080 also stimulated a small negative Isc, consistent with electrogenic K+ secretion. 7. Association of K+ absorption, K+ secretion and Cl- secretion is indicated by similarities in transport mechanism and by secretagogue regulation. In particular, maximal rates of K+ secretory current require uptake via apical membrane K+ pumps. Such interrelations support a common cellular locus for these ion transport pathways

Apical Membrane Chloride Channels in a Colonic Cell Line Activated by Secretory Agonists

We characterized the anion channel responsible for the increase in apical membrane Cl secretion using a model salt-secreting epithelium, the T84 colonic cell line. The adenosine 3\u27,5\u27-cyclic monophosphate (cAMP)-mediated secretagogues, prostaglandin E2, forskolin, and 8-bromo-cAMP, evoked activity of an outwardly rectifying Cl channel in previously quiet cell-attached membrane patches. The channel remained active in excised, inside-out membranes, where its single-channel conductance was 40-45 pS at 0 mV with 160 mM NaCl in pipette and bath. Selectivities were PCl/PNa = 50 and for halides I(1.8)/Br(1.4)/Cl(1.0)/F(0.4). This halide sequence illustrates that the ability of various anions to undergo transepithelial secretion is determined by the selectivity of the basolateral membrane Cl entry step rather than by the apical Cl channel. Open-channel probability increased with depolarization, an effect that would adjust the rate of Cl exit across secretory cell apical membranes with agonist-induced changes in apical membrane potential. Comparison with the properties of Cl channels detected in other cell types suggests that this cAMP-stimulated Cl channel is uniquely present in the apical membranes of salt-secreting epithelial cells

Biophysical Properties of a Chloride Channel in the Apical Membrane of a Secretory Epithelial Cell

1. Patch clamp studies on colonic tumor cell line T84 show the presence of chloride channels. 2. The channels are activated by forskolin, PGE2, or 8-Br-cAMP. 3. Single channel conductance was ca 40 pS at the reversal potential, increasing to 70 pS at +80mV and decreasing to 25 pS at −80 mV. 4. Relative permeabilities were I \u3e Br \u3e Cl \u3e F