Studies on the in vivo sensitivity of spindle microtubules to calcium ions and evidence for a vesicular calcium-sequestering system.
Open Access
- 1 March 1981
- journal article
- research article
- Published by Rockefeller University Press in The Journal of cell biology
- Vol. 88 (3), 604-617
- https://doi.org/10.1083/jcb.88.3.604
Abstract
Ca ions were microinjected into echinoderm [Lytechinus variegatus, L. pictus, Asterias forbesi and Echinarachnius parma] eggs during mitosis to determine the Ca sensitivity of microtubules (Mts) in vivo. Spindle birefringence (BR), a measure of the number of aligned Mts in the spindle, is locally, rapidly and reversibly abolished by small volumes of microinjected CaCl2 (1 mM). Rapid return of BR is followed by anaphase and subsequent divisions are normal. Similar doses of MgCl2, BaCl2, KCl, NaCl, pH buffers, distilled water, or vegetable oil have no effect on spindle BR; large doses of such agents sometimes cause slow, uniform loss in BR over the course of a minute or more. Of the ions tested, only Sr2+ causes effects comparable to Ca2+. Ca-EGTA [ethylene glycol bis (.beta.-aminoethyl ether)N,N,N'',N''-tetraacetic acid] buffers, containing greater than micromolar free Ca2+, abolishes BR in a manner similar to millimolar concentrations of injected CaCl2. Caffeine, a potent uncoupler of the Ca2+-pump/ATPase of sarcoplasmic reticulum, causes a local, transient depression in spindle BR in the injected region. Injection of K-oxalate results in the formation of small, highly BR crystals, presumably Ca-oxalate, in Triton-sensitive compartments in the cytoplasm. Spindle Mts are sensitive to levels of free Ca2+ in the physiological range, show the existence of a strong cytoplasmic Ca2+-sequestering system and support the notion that Mt assembly and disassembly in local regions of the spindle may be orchestrated by local changes in the cytoplasmic free Ca2+ concentration during mitosis. An appendix offers the design of a new chamber for immobilizing echinoderm eggs for injection, a new method for determining the volume of the injected solution and a description of the microinjection technique, which was designed, but never fully described, by Hiramoto.This publication has 59 references indexed in Scilit:
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