UBC Theses and Dissertations
The role of carbonic anhydrase in acid secretion and calcium uptake by the chorioallantoic membrane of the chick embryo Virta, Valerie J.
The major source of calcium for the developing chick embryo is the eggshell. However, the actual mechanism of calcium solubilization from the shell is unknown. The temporal correlation of carbonic anhydrase activity to calcium movement implies that an acidic environment is essentail. To clarify the role of carbonic anhydrase in calcium solubilization and uptake by the chorioallantoic membrane of the chick embryo treatment effects on embryo development, carbonic anhydrase activity and calcium and pH levels were investigated. The treatments consisted of solutions of acid, base, calcium and strontium chlorides, and the enzyme inhibitor-acetazolamide.Experimental sampling was conducted from eleven to sixteen days of incubation. The treatments were administered daily by dipping the eggs into a treatment solution with subsguent sampling on the following day. The acid treatment solution produced a significant (P≤0.05) increase in calcium solubilization and a decrease in carbonic anhydrase activity from the control levels. The base treatment solution produced a significant decrease in calcium solubilization and an increase in carbonic anhydrase activity from the control levels. The calcium chloride treatment solution (providing a partial source of a calcium non-carbonate compound) and the strontium chloride treatment solution (providing a partial source of a non-calcium non-carbonate compound) showed no overall effect on embryonic calcium concentrations. However, there was a decrease in carbonic anhydrase activity from that of the control. This decrease did not appear to be due to a calcium mediated process but was more sensitive to changes in bicarbonate or carbonate levels. Treatments with acetazolamide demonstrated that there was a decrease in carbonic anhydrase activity and also a decrease in calcium transported. However, when an acid treatment was combined with the acetazolamide treatment, calcium was transported even though carbonic anhydrase activity was greatly suppressed. These results confirm that carbonic anhydrase activity appears to be fimctioriing in calcium solubilization and maintenance of the embryonic acid-base balance. It does not appear that the enzyme functions primarily in the transport of calcium across the chorioallantoic membrane.