Abstract
Published work has shown that endothelin-1-induced contractility of bovine retinal pericytes is reduced after culture in high concentrations of glucose. The purpose of the present study was to establish the profile of endothelin-1-induced calcium transients in pericytes and to identify changes occurring after culture in high concentrations of glucose. Glucose had no effect on basal levels of cytosolic calcium or on endothelin-1-induced calcium release from intracellular stores. However, influx of calcium from the extracellular medium after endothelin-1 stimulation was reduced in pericytes that had been cultured in 25 mM D-glucose. L-type Ca(2+) currents were identified by patch clamping. The L-type Ca(2+) channel agonist, (-)-Bay K8644, caused less influx of calcium from the extracellular medium in pericytes that had been cultured in 25 mM D-glucose than in those cultured with 5 mM D-glucose. However, 3-O-methylglucose, a nonmetabolizable analogue of glucose which can cause glycation, had similar effects to those of high concentrations of glucose. The results suggest that reduced function of the L-type Ca(2+) channel that occurs in bovine retinal pericytes after culture in high concentrations of D-glucose is probably due to glycation of a channel protein.
Highlights
Published work has shown that endothelin-1-induced contractility of bovine retinal pericytes is reduced after culture in high concentrations of glucose
These observations indicate that a large portion of the ET-1-induced rise in [Ca2ϩ]i in bovine retinal pericyte (BRP) was due to influx from the extracellular medium
Characterization of Ca2ϩ Channels in the Plasma Membrane of BRP—(Ϫ)-Bay K8644 (10 –20 M) generated an enhanced inward current that activated at Ϫ30 mV and peaked at ϩ10 mV (107 Ϯ 70 pA) (Fig. 3). 30% of those cells showing stable patches had transient inward currents of 10 –200 pA that activated at Ϫ30 mV and peaked at 0 to ϩ10 mV (Fig. 4)
Summary
Published work has shown that endothelin-1-induced contractility of bovine retinal pericytes is reduced after culture in high concentrations of glucose. The purpose of the present study was to establish the profile of endothelin-1-induced calcium transients in pericytes and to identify changes occurring after culture in high concentrations of glucose. The results suggest that reduced function of the L-type Ca2؉ channel that occurs in bovine retinal pericytes after culture in high concentrations of D-glucose is probably due to glycation of a channel protein. We have previously shown [7] that exposure to high ambient glucose concentrations in vitro caused a reduction in the contractile response of the bovine retinal pericyte (BRP) to ET-1. The aim of the present study was 1) to establish the profile of ET-1-induced changes in cytosolic calcium concentrations ([Ca2ϩ]i) in the cultured pericyte and 2) to determine whether prior exposure to raised concentrations of glucose would alter ET-1-induced calcium transients in these cells
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