Table 2.

Effects of insulin and elevated D-glucose on L-arginine transport, membrane potential and intracellular Ca²⁺ in human umbilical vein endothelial cells isolated from gestational diabetic pregnancies

Condition	L-Arginine transport (pmol (μg protein)−1 min−1)	TPP+ influx (pmol (106 cells)−1 min−1)	Membrane potential (mV)	[Ca2+]i (nM)
Non-diabetic cells
5 mm D-glucose †	3·3 ± 0·5 *	0·49 ± 0·07 *	-67·2 ± 0·4 *	46 ± 12 *
Diabetic cells
5 mm D-glucose	5·1 ± 0·2	0·80 ± 0·1	-79·4 ± 0·9	165 ± 25
5 mm D-glucose + insulin	3·7 ± 0·4 *	0·42 ± 0·04 *	n.d.	n.d.
25 mm D-glucose	6·9 ± 0·6	0·78 ± 0·07	-78·5 ± 0·5	146 ± 22
25 mm D-glucose + insulin	5·9 ± 0·3	0·69 ± 0·02	n.d.	n.d.

Human umbilical vein endothelial cells isolated from gestational diabetic pregnancies were cultured initially in M199 containing 20 % serum and either 5 or 25 mm D-glucose in the absence or presence of 1 nM human insulin (added during the last 8 h of a 24 h incubation period). Pretreated confluent third passage endothelial cell monolayers were then washed and incubated in Krebs solution, and contents of protein and DNA, cell number and cell volume measured. Incorporation of L-[³H]leucine and [³H]thymidine was measured over 24 h in actively replicating cells. Values denote the means ± s.e.m. of 3-4 different cell cultures.

^*P < 0·05 relative to values in diabetic endothelial cells in 5 or 25 mm D-glucose or 25 mm D-glucose + insulin. Values for [³H]thymidine incorporation in diabetic cells are all significantly (P < 0·02) lower than non-diabetic cells cultured in 5 mm D-glucose.

^†Paired data in endothelial cells obtained from non-diabetic pregnancies and cultured in 5 mm D-glucose. n.d., not determined.