CALCIUM AND PROTON BUFFERING AND DIFFUSION IN ISOLATED CYTOPLASM FROM MYXICOLA AXONS

被引:47
作者
ABERCROMBIE, RF
HART, CE
机构
[1] EMORY UNIV, SCH MED, DEPT PHYSIOL, ATLANTA, GA 30322 USA
[2] EMORY UNIV, SCH MED, DEPT ANAT, ATLANTA, GA 30322 USA
来源
AMERICAN JOURNAL OF PHYSIOLOGY | 1986年 / 250卷 / 03期
关键词
D O I
10.1152/ajpcell.1986.250.3.C391
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
Ion-selective electrodes recorded the pH (7.49 .+-. 0.05, n = 8) and pCa (6.72 .+-. 0.03, n = 40) in samples (.apprx. 1 .mu.l) of isolated Myxicola axoplasm mounted within 760-.mu.m diameter plastic tubes. We determined the interactions between Ca2+ and H+ on axoplasmic buffers by microinjecting CaCl2 or HCl into the axoplasmic samples at a distance 75-125 .mu.m from the tips of the electrodes (distance = r). When axoplasmic pH was lowered 0.97 .+-. 0.095 from its resting value (measured at r = 125 .mu.m) by injecting 4 nmol HCl, pCa dropped 0.30 .+-. 0.05 (n = 6). When expressed in units of concentration, these data show that a HCl injection of .apprx. 4 mmol/l axoplasm increased H+ and Ca2+ activity by .apprx. 0.3 .mu.M. Lowering axoplasmic pCa 2.20 .+-. 0.43 (r = 75 .mu.m)(n = 3) by injecting 40 pmol CaCl2 had only a small effect on pH. In other experiments, two Ca2+ electrodes measured the Ca2+ activity 125 and 375 .mu.m from the site of CaCl2 injection. Evidence of Ca2+ buffering was obtained when the Ca2+ activity at these two locations was below that expected for simple Ca2+ diffusion away from the injection site. Centrifuged axoplasm (100,000 g) taken from the bottom of the centrifuge tube had a somewhat greater Ca2+ buffering capacity than that taken from the top of the tube. Electron microscopic studies of the centrifuged axoplasm showed a greater concentration of mitochondria and other axoplasmic vesicles in the bottom of the centrifuge tube. Ruthenium red (20-40 .mu.g/ml) greatly reduced Ca2+ buffering. The mitochondrial inhibitors CN (2 mM) and oligomycin (a mixture of oligomycin A, B, and C, 5 .mu.g/ml) also reduced Ca2+ buffering but were not as effective as ruthenium red. Axoplasm in which ATP and mitochondrial substrates were removed by dialysis was unable to lower free Ca2+ when the concentration of this ion was elevated to .apprx. 10 .mu.M. In the presence of oligomycin to block mitochondrial ATPase, and with Mg2+-ATP as the only source of energy, axoplasm lowered Ca2+ activity slowly; with succinate as the only metabolic substrate, axoplasm rapidly lowered the Ca2+ activity from .apprx. 10 .mu.M to below 1 .mu.M.
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页码:C391 / C405
页数:15
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