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A Model Of The Flow of Goods Through A Market Center
Several archaeologists (Binford 1977; Goodyear, Raab and Klinger 1978) have recently called for the creation of "middle range theory" in archaeology. By this term they mean the establishment of a body of theory which will help bridge the interpretive gap between static archaeological facts and the dynamic past phenomena responsible for them. This body of theory would encompass such considerations as natural and cultural formation processes (Schiffer 1976; Sullivan 1978). In response to this exhortation I offer the following discussion and model of the flow of goods through a market center
Voltage-activated proton currents in human lymphocytes
Voltage-activated proton currents are reported for the first time in human peripheral blood T and B lymphocytes and in the human leukaemic T cell line Jurkat E6-1. The properties of H+ currents studied using tight-seal voltage-clamp recording techniques were similar in all cells. Changing the pH gradient by one unit caused a 47 mV shift in the reversal potential, demonstrating high selectivity of the channels for protons. H+ current activation upon membrane depolarisation had a sigmoidal time course that could be fitted by a single exponential function after a brief delay. Increasing pHo shifted the activation threshold to more negative potentials, and increased both the H+ current amplitude and the rate of activation. In lymphocytes studied at pHi 6.0, the activation threshold was more negative and the H+ current density was three times larger than at pHi 7.0. Increasing the intracellular Ca2+ concentration to 1 Ī¼m did not change H+ current amplitude or kinetics detectably. Extracellularly applied Zn2+ and Cd2+ inhibited proton currents, slowing activation and shifting the voltageāactivation curve to more positive potentials. The H+ current amplitude was 100 times larger in CD19+ B lymphocytes and in Jurkat E6-1 cells than in CD3+ T lymphocytes. Following stimulation with the phorbol ester PMA, the H+ current density in peripheral blood T lymphocytes and Jurkat T cells increased. In contrast, the H+ current density of phorbol ester (PMA)-stimulated B lymphocytes was reduced and activation became slower. The pattern of expression of H+ channels in lymphocytes appears well suited to their proposed role of charge compensation during the respiratory burst