. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 40 60 TIME (MIN) Figure 7. Extracellular pH and pCa measured with stationary ion specific electrodes placed close to the calcined surface of a cell under non-calcifying conditions. (A) Positive correlation between pH and pCa, probably caused by increased CaCO, dissolution or leaching at low pH. (B) Anticorrelation between pH and pCa. suggesting calcium-proton ex- change. 2H+/Ca2+ exchange must also be sufficient to overcome the decrease in pericellular Ca2+ at high pH. caused by reductions in CaCO, dissolution and Ca2+ leach
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 40 60 TIME (MIN) Figure 7. Extracellular pH and pCa measured with stationary ion specific electrodes placed close to the calcined surface of a cell under non-calcifying conditions. (A) Positive correlation between pH and pCa, probably caused by increased CaCO, dissolution or leaching at low pH. (B) Anticorrelation between pH and pCa. suggesting calcium-proton ex- change. 2H+/Ca2+ exchange must also be sufficient to overcome the decrease in pericellular Ca2+ at high pH. caused by reductions in CaCO, dissolution and Ca2+ leaching from the cell wall. Thermodynamics The maximum pH observed at the alkaline surface us- ing microelectrodes approaches the thermodynamic limit for ATP driven 2H+/Ca:+ exchange, calculated using eq. 3 (Fig. 8). The approach is closest at high solution Ca2+ activities (low pCa). As pCa:+ increases, the maximum pH also increases, although not as much as allowed by thermodynamics. At pCa >4, higher pH readings are ob- tained in the presence of the weak Ca2+ buffer citrate, suggesting that the rate of Ca2+ supply to the cell may limit proton uptake. All pericellular pH, pCa observations fall within the thermodynamic constraints for ATP driven 2H+/Ca2+ exchange, and the Ca2+ dependence for peri- cellular pH provides some support for the Ca2+ ATPase model. The pH and pCa in large culture vessels containing Cham also approach the calculated thermodynamic limits for 2H+/Ca:+ exchange (Fig. 8). The most extreme con- ditions observed (pH , pCa ) are close to the most extreme conditions observed at the cell surface with microelectrodes. Rather high pericellular pH (about ) is observed transiently in Ca2+ free solutions, but pH banding eventually collapses, consistent with a Ca2+ re- quirement for banding. Internal Ca24 stores, perhaps sup- plemented by CaCO, dissolution and Ca2+ leaching from the cell wall, may support banding for awhile. Extracellular electrical current
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
