The effect of endotoxin on neonatal erythrocyte intracellular calcium concentration

Erythrocyte membrane deformability is dependent on the maintenance of "normal" intracellular calcium (Ca) levels. Red cell flexibility is known to be altered in the septic neonate. In turn, this adversely affects viscosity and compromises flow in the microcirculation. It has been suggested that this may play a role in the mesenteric hypoperfusion associated with necrotizing enterocolitis. This study was designed to determine the effect of endotoxin on erythrocyte Ca homeostasis in the neonate. Paired specimens were obtained from the umbilical cord of 10 healthy neonates. The samples were incubated with either buffered saline (control) or 2 micrograms/mL of Escherichia coli endotoxin (LPS). Erythrocytes were then isolated, washed, and loaded with the fluorescent Ca chelator, FURA-2. The free cytosolic Ca concentration was determined by spectroscopic analysis of the ratio of fluorescent intensities at 340 nm and 380 nm. Results were obtained every 1.8 seconds for 1 minute, and the mean value was used for analysis. In 10 additional neonates, the white blood cells were removed before incubation in saline and LPS, and the erythrocytes were evaluated as described above. Differences were analyzed statistically by the paired t test. In the presence of white blood cells, endotoxin resulted in a significant increase in free cytosolic Ca concentration (LPS, 42.602 +/- 5.166 nmol; control, 31.661 +/- 4.002 nmol; P < .02). However, no significant difference were detected when cells were incubated in the absence of white blood cells (LPS, 32.374 +/- 2.479 nmol; control, 34.021 +/- 2.549 nmol). Endotoxin induces a significant increase in neonatal free cytosolic Ca concentration.(ABSTRACT TRUNCATED AT 250 WORDS)