A Cation–π Interaction between Extracellular TEA and an Aromatic Residue in Potassium Channels

Open-channel blockers such as tetraethylammonium (TEA) have a long history as probes of the permeation pathway of ion channels. High affinity blockade by extracellular TEA requires the presence of an aromatic amino acid at a position that sits at the external entrance of the permeation pathway (residue 449 in the eukaryotic voltage-gated potassium channel Shaker). We investigated whether a cation–{pi} interaction between TEA and such an aromatic residue contributes to TEA block using the in vivo nonsense suppression method to incorporate a series of increasingly fluorinated Phe side chains at position 449. Fluorination, which is known to decrease the cation–{pi} binding ability of an aromatic ring, progressively increased the inhibitory constant Ki for the TEA block of Shaker. A larger increase in Ki was observed when the benzene ring of Phe449 was substituted by nonaromatic cyclohexane. These results support a strong cation–{pi} component to the TEA block. The data provide an empirical basis for choosing between Shaker models that are based on two classes of reported crystal structures for the bacterial channel KcsA, showing residue Tyr82 in orientations either compatible or incompatible with a cation–{pi} mechanism. We propose that the aromatic residue at this position in Shaker is favorably oriented for a cation–{pi} interaction with the permeation pathway. This choice is supported by high level ab initio calculations of the predicted effects of Phe modifications on TEA binding energy

A model of labour allocation decision-making in peasant-type households

The extent of the food crisis in Sub-Saharan Africa is generating a renewed interest in the role of peasants in addressing the food problem. This paper is premised on the view that policy action with respect to agriculture development in Africa requires a realistic model of how rural peasants make decisions. In the first part of the paper we construct a model of such decision-making. The model focuses on peasant-type households as described and analysed by Chayanov. A central characteristic of such households is their attempt to seek a total of satisfactions, as producing and consuming units, rather than the pursuit of profit maximisation inherent in many microeconomic models of rural households. In the attempt to achieve its objectives, the household must make decisions concerning the allocation of its principal productive resource, labour. The model outlines the manner in which labour allocation decisions are made, subject to plausible constraints operating on rural households in Africa. The second part of the paper examines some of the implications of this model for various rural development policies

Climigration? Population and climate change in Arctic Alaska

Residents of towns and villages in Arctic Alaska live on “the front line of climate change.” Some communities face immediate threats from erosion and flooding associated with thawing permafrost, increasing river flows, and reduced sea ice protection of shorelines. The term climigration, referring to migration caused by climate change, originally was coined for these places. Although initial applications emphasized the need for government relocation policies, it has elsewhere been applied more broadly to encompass unplanned migration as well. Some historical movements have been attributed to climate change, but closer study tends to find multiple causes, making it difficult to quantify the climate contribution. Clearer attribution might come from comparisons of migration rates among places that are similar in most respects, apart from known climatic impacts. We apply this approach using annual 1990–2014 time series on 43 Arctic Alaska towns and villages. Within-community time plots show no indication of enhanced out-migration from the most at-risk communities. More formally, there is no significant difference between net migration rates of at-risk and other places, testing several alternative classifications. Although climigration is not detectable to date, growing risks make either planned or unplanned movements unavoidable in the near future

Multicellular Root Hairs on Adventitious Roots of Kalanchoe Fedtschenkoi

Author Institution: Department of Botany and Plant Pathology, The Ohio State University, Columbus 1

The central theme of American agricultural history

"American agricultural history is not only the story of change. Tradition has also been important. An agrarian tradition took shape in the eighteenth and nineteenth centuries that exalted farming and rural life, looking upon them as having great importance for the nation's welfare."--First page.Richard S. Kirkendall*, Henry A. Wallace (Professor of History, Iowa State University)New 2/84/5

Book Reviews

Book Reviews of: Carol Tavris, Anger: The Misunderstood Emotion (Simon & Schuster, 1982) John Fowles, A Maggot (Little-Brown, 1985) James Q. Wilson and Richard J. Herrnstein, Crime and Human Nature (Simon & Schuster, 1985