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COLCHICINE BINDING IN TISSUE SLICES : Decrease by Calcium and Biphasic Effect of Adenosine-3',5'-Monophosphate

The Journal of Cell Biology
The Rockefeller University Press
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COLCHICINE BINDING IN TISSUE SLICES Decrease by Calcium and Biphasic Effect of Adenosine-3', 5'-Monophosphate ELIZABETH GILLESPIE. From the Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510 INTRODUCTION vitro . Under appropriate conditions changes in colchicine binding should reflect changes in the microtubule-subunit equilibrium . The effects of both cAMP and calcium on colchicine binding were examined. Calcium was included in this study, for two reasons . First, it is necessary for some of the functions that have been linked with micro- tubules, and second, cAMP is known to alter calcium metabolism (21) . The results obtained show that both cAMP and calcium alter colchicine binding to soluble material in liver, pancreas, and spleen. A preliminary account of a portion of this work has appeared (10) . In the past few years microtubules have been implicated in an ever increasing number of func- tions . In addition to their roles in the mitotic spindle and in cilia and flagella, evidence has accumulated suggesting their involvement in (a) the aggregation of platelets (24), (b) degranula- tion and secretion (11, 14, 15, 19), (c) melanin granule movement (18), (d) chemotaxis (5), and (e) axonal flow (6) . Many of these functions are affected by cyclic adenosine-3', 5'-monophosphate (cAMP).I Direct or indirect evidence suggests that cAMP (a) inhibits platelet aggregation (20), (b) disperses melanin granules (3), and (c) causes the release of several compounds stored in granules (2, 9, 13, 17) . This uxtaposition of cAMP and microtubules suggested that possibly cAMP might affect the functions in question by acting on the motile sys- tem which involves microtubules. To test this idea, a biochemical approach to the study of micro- tubules in situ has been developed . It is based on the fact that formed microtubules are in equi- librium with depolymerized subunits (see below), an

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