Neural plate microvillus lengthening in rat embryos grown in various concentrations of glucose and further studies of the mechanism.

Glucose is an important cellular nutrient, and in the early embryo, which is dependent mostly on anaerobic glycolysis, it is even more essential. Based on tissue culture cells in which glucose utilization has become membrane-limited, a concept has been developed that the tip of the microvilli is the entrance compartment for glucose and that the shaft sets up a diffusion barrier. An increase in length of the microvillus is associated with decreased entry of phosphorylated hexose into the cells. Our previous findings of lengthening of the microvilli of the neural plate cells after 40 min exposure to glucose at room temperature have been extended to a 17 hr whole embryo culture system. In cultures where the final concentration of glucose was 20 and 24 mg/dl there was embryonic death. In those cultures ending with 29-137 mg/dl of glucose the embryos developed normally. Those grown in dialyzed serum supplemented with B vitamins and glucose grew equally as well as those in whole rat serum. Somite numbers attained did not change with increasing glucose concentration but a modest increase in micromoles of glucose used per embryo was found, suggesting the presence of another source of energy at lower glucose concentrations. The average glucose utilization per gram of protein per hour was 844 mumol in these day 9.5-10 embryos and this compares to 733 mumol previously found using uniformly labeled 14C glucose on day 10.3. Lactate production averaged 85% of the glucose utilized. Pyruvate did not support growth in the absence of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)