This finding may indicate a role of ET in POAG or ocular antihypertensive treatment, and its relevance should be further investigated.

Endothelin-like immunoreactivity was detected in human (15.6 +/- 2.7 pg/ml) and bovine (11.1 +/- 0.98 pg/ml) aqueous humour of the eye. These concentrations are 2-3 times higher than the corresponding plasma levels. Cultured human nonpigmented ciliary epithelial cells released endothelin-like immunoreactivity with a maximum of 2.1 +/- 0.32 pg/(cm2* 48 h). The release was stimulated by fetal calf serum, thrombin, carbachol and phorbol ester and blocked by cycloheximide. Immunocytochemistry showed cytoplasmic staining of cultured human nonpigmented ciliary epithelial cells for endothelin-1. Endothelin-1 was shown to induce contractions in isolated human ciliary muscle by isometric force measurements. Endothelin in the aqueous humour may play a role in the regulation of intraocular pressure.

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The function of plasma membrane as control point of glucose metabolism has been studied in confluent monolayer of C1300 neuroblastoma (N2A) and glioma (C6) cells. In neuroblastoma, steady state intracellular glucose concentration reached the extracellular levels, while intracellular contents in C6 glioma cells remained very low. In C6 glial cells the amount of glycogen as source of energy was much higher than that found in C1300 neuroblastoma cells. Influx rates of D-glucose in C6 glioma cells were only half those found in neuroblastoma cells. During the influx period (0-40 s) the transport of glucose in these cells did not exceed the phosphorylation rate, whereas a steady, time-dependent increase in glucose content was observed in neuroblastoma cells. While glucose uptake in neuroblastoma cells seems to be regulated at the level of phosphorylating enzymes, the control point in C6 glioma is believed to be membrane transport.

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