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Title:Amiloride-sensitive components of sodium transport in guinea pig red blood cells: A cause of imbalance of sodium ion at low temperature
Author(s):Zhao, Zhihong
Doctoral Committee Chair(s):Willis, John S.
Department / Program:Biology, Animal Physiology
Biology, Zoology
Discipline:Biology, Animal Physiology
Biology, Zoology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Animal Physiology
Biology, Zoology
Abstract:It has previously been found that gaining of Na in red cells of guinea pig is faster than in those of ground squirrel during cold storage at 5$\sp\circ$C in vitro and amiloride can partially inhibit the accumulation. Also, amiloride-sensitive Na influx in guinea pig red cells is known to be larger at 20$\sp\circ$C than at 37$\sp\circ$C.
In this study, it is shown that amiloride-sensitive Na influx in guinea pig red blood cells can be activated by cytoplasmic H$\sp+$ and it is correlated with cation-dependent H$\sp+$ loss from acidified cells. It is also stimulated by shrinkage and by phorbol ester in the presence of Ca, as is Na-H exchange in other cells. Aside from this apparent Na-H exchange, there are at least one and possibly two other distinct components of amiloride-sensitive Na influx: one is hypertonically induced, with a high sensitivity to amiloride and with low sensitivity to Na; the other appears to represent Na-Mg exchange.
Comparison between results at 37$\sp\circ$C and 20$\sp\circ$C shows that amiloride-sensitive Na influx can be activated dramatically by the activators of Na-H exchange at 37$\sp\circ$C, but not at 20$\sp\circ$C. Cell alkalinization can diminish the elevation of amiloride-sensitive Na influx at 20$\sp\circ$C, while depletion of cell magnesium can not. These observations lead to the conclusion that cooling-induced amiloride-sensitive Na influx in guinea pig cells is mainly due to the increased activity of the Na-H exchange mechanism.
By measurement of the stimulation of amiloride-sensitive Na influx by cytoplasmic H$\sp+,$ the affinity of the amiloride-sensitive Na-H exchanger to cytoplasmic H$\sp+$ is found to be higher at 20$\sp\circ$C than at 37$\sp\circ$C. In cells incubated in Na-free medium at 37$\sp\circ$C ("reversed Na gradient"), acidification increased amiloride-sensitive Na efflux, indicating the presence of a cytoplasmic regulatory site for H$\sp+.$ At 20$\sp\circ$C, acidification caused no significant increase, but basification inhibited Na efflux into Na-free medium, indicating higher sensitivity of the regulatory site to cytoplasmic H$\sp+.$ Thus increased activity of the Na-H exchange at reduced temperature is characterized by reduced H$\sp+$ transport but increased affinity of a regulatory site for H$\sp+.$
Issue Date:1991
Rights Information:Copyright 1991 Zhao, Zhihong
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9211058
OCLC Identifier:(UMI)AAI9211058

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