Hussain, Ali Aijaz; (1990) Taurine, photoreceptors and retinitis pigmentosa. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Taurine, photoreceptors and retinitis pigmentosa. Various aspects of taurine homeostasis have been studied in man and animals with inherited and induced photoreceptor abnormalities. Platelets from patients with retinitis pigmentosa (RP) were incubated in Ca^{2+} -free Krebs' bicarbonate medium containing 1 μM or 60 μM H-taurine, and in autologous plasma. Although, in general, the platelets showed normal taurine uptake, the capacity of the higher affinity carrier was reduced in patients with autosomal dominant (AD) RP showing regional expression (R-type). Uptake was reduced when platelets from X-hemizygotic and AD R-type patients were incubated in autologous plasma. The concentration of taurine was higher than normal in plasma from patients with X-heterozygote and AD R-type RP. Erythrocyte osmotic fragility was also increased but the concentrations of plasma vitamin E and erythrocyte glutathione were normal. Delivery of systemic taurine to photoreceptor cells is dependent upon a transport system in the retinal pigment epithelium (RPE). The capacity for H-taurine uptake has, therefore, been monitored in RPE and retina from donated human eyes. The potential for postmortem survival was assessed with baboon tissue. The photoreceptor less retinas of RP donors retained an inner retinal transport system for taurine which was always reduced in the pigmented, 'bone-spicular' region (PA): kinetic analysis suggested disparate carriers in the PA and non-PA. Taurine uptake by the RPE was reduced in all RP eyes examined. Comparing tissue from over PA and non-PA retina. Km's were similar but Vmax's in PA RPE were greatly reduced. Taurine uptakes by the retina and pigment epithelium from Abyssinian cats with a dominant gene leading to early onset photoreceptor degeneration were also studied and found to be normal. Oral administration of taurine to albino Wistar rats did not prevent photoreceptor degeneration induced by continuous exposure to high intensity fluorescent light; sane protection with respect to changes in retinal amino acids were noted. No substantial evidence has been obtained to suggest that taurine deficiency is a primary cause of photoreceptor degeneration in the diseases studied here. However, it is very likely to be involved in secondary mechanisms leading to photoreceptor cell loss.

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