Calcium diffusion coefficient in Myxicola axoplasm.
Calcium diffusion coefficients were measured in Myxicola axoplasm and in agar controls by two independent techniques: one utilizing 45Ca, and one utilizing Ca-specific mini-electrodes. The lowest value, approximately 0.1 x 10(-6) cm2.s-1, was measured, using the mini-electrode technique, in axoplasm with intact Ca-sequestering organelles. With ATP-depleted axoplasm, diffusion coefficients of 0.5-2 x 10(-6) cm2.s-1 were obtained by both isotope and mini-electrode techniques. In organelle-free axoplasm with a protein concentration roughly half that in the intact axoplasm, diffusion coefficients of 1.4-3 x 10(-6) cm2.s-1 were measured at 0.7 microM Ca and 7 x 10(-6) cm2.s-1 at 3-5 microM Ca. When compared with measurements of the calcium buffering capacity [Al-Baldawi NF. Abercrombie RF. (1995) Cytoplasmic Ca buffer capacity determined with Nitr-5 and DM-nitrophen. Cell Calcium, 17, 409-422], these diffusion coefficients require that part of the buffer capacity be located on mobile Ca-binding sites.
al-Baldawi
N F
NF
Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, USA.
Abercrombie
R F
RF
D000362:Agar; D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D003956:Dialysis; D004058:Diffusion; D004563:Electrochemistry; D004566:Electrodes; D015388:Organelles / Q000378:metabolism; D011077:Polychaeta
D000362:Agar; D002118:Calcium