Calcium accumulation by organelles within Myxicola axoplasm

N. F. Al-Baldawi, J. E. Moore, R. F. Abercrombie

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Abstract

1. 45Ca2+ accumulation into inulin-inaccessible compartments within cytoplasm from the giant axon of Myxicola infundibulum was measured as a function of free calcium, pH, and time. Accumulation reached a maximum after 1 h and remained stable for at least 3 h. 2. At 0.5, 5, and 50 μM [Ca2+], in the presence of 1 mM ATP or 5 mM succinate steady-state calcium uptake had a bell-shaped dependence on pH with a maximum near pH 7. Uptake was abolished by the proton uncoupling reagent carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP, 4 μg ml-3 3. Uptake of the membrane permeant cation, [14C]-tetraphenylphosphonium (TPP+), also had a bell-shaped dependence on pH with a maximum pH ~ 7, suggesting a pH dependence of the electrical potential of a membrane enclosed cytoplasmic compartment. Cyanide (2 mM) inhibited TPP+ uptake. 4. Inositol 1,4,5-trisphosphate (IP3, 10 μM), reduced steady-state calcium accumulation by 20-22% at 0.5 μM free calcium, pH 7 (P < 0.01, n = 16) and at 5 μM free calcium, pH 8 (P < 0.0005, n = 35). No effects of IP3 were found at other pH or calcium concentrations. 5. Neither guanosine 5'-triphosphate (GTP) nor inositol 1,3,4,5-tetrakisphosphate (IP4) had an effect on calcium uptake (5 μM [Ca2+], pH 8). 6. At 0.5 μM free calcium; vanadate (10 μM) inhibited 20-30%, of the 45Ca2+ accumulation, thapsigargin (33 nM) inhibited 20-30%, and cyanide (2 mM) plus oligomycin B (2 μg ml-1), or valinomycin (1 μM), inhibited 70-80%. The fraction of uptake sensitive to thapsigargin fell as the free calcium increased; however, the sensitivity of uptake to cyanide plus oligomycin B was ~ 80% for 0.5, 5.0, and 50 μM [Ca2+]. 7. Thapsigargin had no additional inhibiting effect in the presence of cyanide plus oligomycin B. IP3 had no effect in the presence of cyanide plus oligomycin B or other mitochondrial inhibitors. 8. Results suggest the presence of both mitochondrial (70-80%) and nonmitochondrial (20-30%) calcium pools in this system (at 05-50 μM Ca2+). The apparent non-mitochondrial uptake (sensitive to thapsigargin, or IP3) is not detectable in the presence of mitochondrial inhibitors. We interpret these results as evidence of functional communication between mitochondrial and non-mitochondrial calcium stores.

Original languageEnglish (US)
Pages (from-to)633-646
Number of pages14
JournalJournal of Physiology
Volume461
StatePublished - 1993

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Polychaeta
Organelles
Calcium
Cyanides
Thapsigargin
Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone
Valinomycin
Inositol 1,4,5-Trisphosphate
Vanadates
Inulin
Succinic Acid
Pituitary Gland
Guanosine Triphosphate
Membrane Potentials
Axons
Cations
Protons

ASJC Scopus subject areas

  • Physiology

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Al-Baldawi, N. F., Moore, J. E., & Abercrombie, R. F. (1993). Calcium accumulation by organelles within Myxicola axoplasm. Journal of Physiology, 461, 633-646.

Calcium accumulation by organelles within Myxicola axoplasm. / Al-Baldawi, N. F.; Moore, J. E.; Abercrombie, R. F.

In: Journal of Physiology, Vol. 461, 1993, p. 633-646.

Research output: Contribution to journalArticle

Al-Baldawi, NF, Moore, JE & Abercrombie, RF 1993, 'Calcium accumulation by organelles within Myxicola axoplasm', Journal of Physiology, vol. 461, pp. 633-646.
Al-Baldawi NF, Moore JE, Abercrombie RF. Calcium accumulation by organelles within Myxicola axoplasm. Journal of Physiology. 1993;461:633-646.
Al-Baldawi, N. F. ; Moore, J. E. ; Abercrombie, R. F. / Calcium accumulation by organelles within Myxicola axoplasm. In: Journal of Physiology. 1993 ; Vol. 461. pp. 633-646.
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N2 - 1. 45Ca2+ accumulation into inulin-inaccessible compartments within cytoplasm from the giant axon of Myxicola infundibulum was measured as a function of free calcium, pH, and time. Accumulation reached a maximum after 1 h and remained stable for at least 3 h. 2. At 0.5, 5, and 50 μM [Ca2+], in the presence of 1 mM ATP or 5 mM succinate steady-state calcium uptake had a bell-shaped dependence on pH with a maximum near pH 7. Uptake was abolished by the proton uncoupling reagent carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP, 4 μg ml-3 3. Uptake of the membrane permeant cation, [14C]-tetraphenylphosphonium (TPP+), also had a bell-shaped dependence on pH with a maximum pH ~ 7, suggesting a pH dependence of the electrical potential of a membrane enclosed cytoplasmic compartment. Cyanide (2 mM) inhibited TPP+ uptake. 4. Inositol 1,4,5-trisphosphate (IP3, 10 μM), reduced steady-state calcium accumulation by 20-22% at 0.5 μM free calcium, pH 7 (P < 0.01, n = 16) and at 5 μM free calcium, pH 8 (P < 0.0005, n = 35). No effects of IP3 were found at other pH or calcium concentrations. 5. Neither guanosine 5'-triphosphate (GTP) nor inositol 1,3,4,5-tetrakisphosphate (IP4) had an effect on calcium uptake (5 μM [Ca2+], pH 8). 6. At 0.5 μM free calcium; vanadate (10 μM) inhibited 20-30%, of the 45Ca2+ accumulation, thapsigargin (33 nM) inhibited 20-30%, and cyanide (2 mM) plus oligomycin B (2 μg ml-1), or valinomycin (1 μM), inhibited 70-80%. The fraction of uptake sensitive to thapsigargin fell as the free calcium increased; however, the sensitivity of uptake to cyanide plus oligomycin B was ~ 80% for 0.5, 5.0, and 50 μM [Ca2+]. 7. Thapsigargin had no additional inhibiting effect in the presence of cyanide plus oligomycin B. IP3 had no effect in the presence of cyanide plus oligomycin B or other mitochondrial inhibitors. 8. Results suggest the presence of both mitochondrial (70-80%) and nonmitochondrial (20-30%) calcium pools in this system (at 05-50 μM Ca2+). The apparent non-mitochondrial uptake (sensitive to thapsigargin, or IP3) is not detectable in the presence of mitochondrial inhibitors. We interpret these results as evidence of functional communication between mitochondrial and non-mitochondrial calcium stores.

AB - 1. 45Ca2+ accumulation into inulin-inaccessible compartments within cytoplasm from the giant axon of Myxicola infundibulum was measured as a function of free calcium, pH, and time. Accumulation reached a maximum after 1 h and remained stable for at least 3 h. 2. At 0.5, 5, and 50 μM [Ca2+], in the presence of 1 mM ATP or 5 mM succinate steady-state calcium uptake had a bell-shaped dependence on pH with a maximum near pH 7. Uptake was abolished by the proton uncoupling reagent carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP, 4 μg ml-3 3. Uptake of the membrane permeant cation, [14C]-tetraphenylphosphonium (TPP+), also had a bell-shaped dependence on pH with a maximum pH ~ 7, suggesting a pH dependence of the electrical potential of a membrane enclosed cytoplasmic compartment. Cyanide (2 mM) inhibited TPP+ uptake. 4. Inositol 1,4,5-trisphosphate (IP3, 10 μM), reduced steady-state calcium accumulation by 20-22% at 0.5 μM free calcium, pH 7 (P < 0.01, n = 16) and at 5 μM free calcium, pH 8 (P < 0.0005, n = 35). No effects of IP3 were found at other pH or calcium concentrations. 5. Neither guanosine 5'-triphosphate (GTP) nor inositol 1,3,4,5-tetrakisphosphate (IP4) had an effect on calcium uptake (5 μM [Ca2+], pH 8). 6. At 0.5 μM free calcium; vanadate (10 μM) inhibited 20-30%, of the 45Ca2+ accumulation, thapsigargin (33 nM) inhibited 20-30%, and cyanide (2 mM) plus oligomycin B (2 μg ml-1), or valinomycin (1 μM), inhibited 70-80%. The fraction of uptake sensitive to thapsigargin fell as the free calcium increased; however, the sensitivity of uptake to cyanide plus oligomycin B was ~ 80% for 0.5, 5.0, and 50 μM [Ca2+]. 7. Thapsigargin had no additional inhibiting effect in the presence of cyanide plus oligomycin B. IP3 had no effect in the presence of cyanide plus oligomycin B or other mitochondrial inhibitors. 8. Results suggest the presence of both mitochondrial (70-80%) and nonmitochondrial (20-30%) calcium pools in this system (at 05-50 μM Ca2+). The apparent non-mitochondrial uptake (sensitive to thapsigargin, or IP3) is not detectable in the presence of mitochondrial inhibitors. We interpret these results as evidence of functional communication between mitochondrial and non-mitochondrial calcium stores.

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