Effect of elevated extracellular glucose concentrations on calcium ion uptake by cultured rat vascular smooth muscle cells.

Blood flow autoregulation is impaired in early diabetes mellitus, predisposing the microvasculature to injury. Blood flow autoregulation is in part a myogenic response that is critically dependent on Ca2+ uptake via voltage-sensitive calcium channels in vascular smooth muscle cells (VSMC). Recent evidence suggests that impairment of blood flow autoregulation in diabetes may be responsive to variations in glycemic control. The present study thus examined the independent effect of an elevated extracellular glucose concentration on Ca2+ uptake by cultured rat VSMC in vitro. A threshold glucose concentration of 15-20 mmol/l markedly and maximally depressed basal and voltage sensitive Ca2+ channel activated (BAY K 8644, 10(-7) M) Ca2+ uptake. This effect was apparent within 3 h of incubating VSMC with the high glucose medium and was maximal after 48 h incubation. Osmotic control media containing either mannitol or L-glucose did not inhibit Ca2+ uptake by VSMC, thus confirming the effect was specific for elevated extracellular glucose concentrations and unrelated to changes in extracellular osmolality. Glucose-induced inhibition of basal and voltage-sensitive transmembrane fluxes of Ca2+ in VSMC may provide a metabolic mechanism for impaired calcium-dependent blood flow autoregulatory responses in early diabetes mellitus.