Acid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission, as well as initiation of pain and neuronal death following ischemic stroke. As such, there... Show moreAcid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission, as well as initiation of pain and neuronal death following ischemic stroke. As such, there is a great interest in understanding the in vivo regulation of ASICs, especially by endogenous neuropeptides that potently modulate ASICs. The most potent endogenous ASIC modulator known to date is the opioid neuropeptide big dynorphin (BigDyn). BigDyn is up-regulated in chronic pain and increases ASIC-mediated neuronal death during acidosis. Understanding the mechanism and site of action of BigDyn on ASICs could thus enable the rational design of compounds potentially useful in the treatment of pain and ischemic stroke. To this end, we employ a combination of electrophysiology, voltage-clamp fluorometry, synthetic BigDyn analogs, and noncanonical amino acid-mediated photocrosslinking. We demonstrate that BigDyn binding results in an ASIC1a closed resting conformation that is distinct from open and desensitized states induced by protons. Using alanine-substituted BigDyn analogs, we find that the BigDyn modulation of ASIC1a is primarily mediated through electrostatic interactions of basic amino acids in the BigDyn N terminus. Furthermore, neutralizing acidic amino acids in the ASIC1a extracellular domain reduces BigDyn effects, suggesting a binding site at the acidic pocket. This is confirmed by photocrosslinking using the noncanonical amino acid azidophenylalanine. Overall, our data define the mechanism of how BigDyn modulates ASIC1a, identify the acidic pocket as the binding site for BigDyn, and thus highlight this cavity as an important site for the development of ASIC-targeting therapeutics. Show less
Many local tenure arrangements in Niger were largely implicit, not recorded in any codified form. In the process of codification now underway, chiefs are regarded as the key interpreters of... Show moreMany local tenure arrangements in Niger were largely implicit, not recorded in any codified form. In the process of codification now underway, chiefs are regarded as the key interpreters of tradition, mutating the implicit into the explicit. Land tenure reform is not without contradictions. How are chiefs to maintain a level of flexibility and dynamism within the codified, rigidified form that the local tenure arrangements will have once they are made explicit? How are chiefs to determine which implicit local customary practice is to have primacy in a codified form, since their parameters are always changing from season to season and from year to year? As the new 'Code rural' in Niger shows, the invention-of-tradition approach which has gained prominence in English-language research has failed in its French counterparts. Both planner-administrators and academics are engaged in a discourse that seems to take tradition as an undisputed given. The remarkable thing is that is appears to work. The 'Code rural' has been considered path-breaking and innovative because it seeks to modernize tenure rules without breaking with tradition. The conclusion is that land tenure legislation can be modernized by integrating traditional chiefs into the legal framework. Show less
