The interrelationships between sodium ion, calcium transport and oxygen utilization in the isolated chick...

The interrelationships between sodium ion, calcium transport and oxygen utilization have been investigated in the chick chorioallantoic membrane. The oxygen uptakes of the two surface layers of the tissue, the ectoderm and the endoderm, were separated into their basal, Na(+) dependent and Ca(++) dependent components. The endoderm has a basal rate of respiration of 3.6 μliters O2/cm(2)/hr and a Na(+) dependent component of 1.4 μliters O2/cm(2)/hr. The ectoderm has a basal rate of respiration of about 3.5 μliters O2/cm(2)/hr, and Na(+) and Ca(++) dependent components of 1.1 and 3.6 μliters O2/cm(2)/hr, respectively. The rate of ectodermal calcium transport and calcium-stimulated oxygen uptake is strictly dependent on the presence of sodium in the bathing medium, and complex kinetics are observed as a function of sodium concentration. On the other hand, in 140MM Na(+) the rate of calcium transport exhibits simple saturation kinetics as a function of calcium concentration. Ca(++)/O2 ratios determined for many different rates of transport give a ratio of about 0.5, a value much lower than similar ratios determined for other transport mechanisms. The calcium transport mechanism in the ectoderm responds to changes in transport rate very sluggishly, taking 30 to 50 min to give a maximum response. The differences between the calcium transport mechanism in this membrane and other known transport systems are discussed and it is suggested that these differences may represent the adaptations necessary for transcellular calcium transport.