EFFECT OF ELEVATED GLUCOSE-CONCENTRATION ON MEMBRANE VOLTAGE REGULATION IN RETINAL CAPILLARY PERICYTES

The influence of elevated glucose concentration on resting membrane vo ltage, electrogenic Na+-K+-ATPase, and ATP-sensitive potassium channel s (K(ATP) channels) was studied in cultured bovine retinal capillary p ericytes using conventional microelectrodes. The resting membrane volt age in cells grown in medium containing 5 mM glucose (control) average d -27 +/- 1.2 mV (mean +/- SE, n = 26) and was not different from cell s grown in medium containing 22.5 mM glucose (-26 1.2 mV, n = 26). Add ition of ouabain (10(-4) M), a specific inhibitor of the Na+-K+-ATPase , depolarized the membrane potential by 3.6 +/- 0.4 mV (n = 10) in cel ls grown under control conditions and 0.7 +/- 0.2 mV (n = 6) in cells grown under elevated glucose conditions. Thus, electrogenic activity o f the Na+-K+-ATPase was significantly (P < 0.0001) reduced to 19% comp ared with control conditions. Electrogenic Na+-K+-ATPase activity coul d be partially restored (ouabain-induced depolarization DELTAV = 2.0 /- 0.2 mV, n = 6) in cells grown with high glucose in the presence of the aldose reductase inhibitor tolrestat (10(-5) M). The potassium cha nnel opener Hoe 234 (10(-6) M) induced membrane potential hyperpolariz ation in control cells (DELTAV = 7.3 +/- 1.2 mV, n = 13), which could be completely inhibited by the K(ATP) channel blocker glibenclamide (1 0(-7) M, n = 5). This indicates that pericytes possess K(ATP) channels . The effect of K(ATP) channels on membrane voltage was not significan tly changed (P = 0.16) in cells cultured under high-glucose conditions (DELTAV = 9.6 +/- 2.0 mV, n = 6). Acute changes of glucose concentrat ion did not affect the membrane voltage (n = 6). We conclude that high glucose concentrations after the activity of the Na+-K+-ATPase in ret inal pericytes via a mechanism involving the polyol metabolism. Theref ore, hyperglycemia may alter regulation of membrane voltage and contra ctility of pericytes and, hence, the regulation of retinal microcircul ation in diabetes. Altered microcirculation could be an important fact or in the pathogenesis of diabetic retinopathy.