Free diffusion coefficient of ionic calcium in cytoplasm

• Published in: Cell calcium (Edinburgh) Vol. 8; no. 6; pp. 437 - 448
• Main Authors: Donahue, Brian S., Abercrombie, R.F.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier India Pvt Ltd 01.12.1987; Elsevier
• Subjects: Animals; Axons - metabolism; Biological and medical sciences; Calcium - metabolism; Calcium Radioisotopes; Cell physiology; Cytoplasm - metabolism; Diffusion; Energy Metabolism; Fundamental and applied biological sciences. Psychology; Ions - metabolism; Membrane and intracellular transports; Microelectrodes; Molecular and cellular biology; Polychaeta; Calcium; Radiolabelling; Axoplasma; Polychaeta; Ions; Binding site; Annelida; Giant neuron; Chelation; Microtubule; Invertebrata; Diffusion coefficient; Diffusion; Cytoplasm
• ISSN: 0143-4160; 1532-1991
• DOI: 10.1016/0143-4160(87)90027-3

The free diffusion coefficient of ionic Ca was measured in isolated samples of Myxicola axoplasm by following the migration of 45Ca. When precautions were taken to minimize the sequestration and chelation of 45Ca (i.e., using inhibitors, energy deprivation, and saturation of Ca chelation sites), a diffusion coefficient of 5.3 × 10 −6 cm 2 s −1 was measured. The diffusion coefficient was not appreciably changed by lowering free calcium from 100 μM to ∼10 μM or by increasing the diffusion time from ten to twenty minutes. In untreated cytoplasm taken directly from the giant axon of Myxicola , the migration of Ca was more complex and could not be described by a single diffusion coefficient. This result is interpreted to suggest that bulk movement of Ca-buffers may occur in untreated Myxicola axoplasm, a system that contains few microtubules.