Altered Expression of Parvalbumin in Neural Retina of the Insulin-dependent Diabetic Rat

Park, Hyo Suk; Park, Sung Jin; Park, Sun Hwa; Chung, Jin Woong; Chun, Myung Hoon; Oh, Su Ja

Abstract

Calcium-binding proteins in the nervous system are functioned in Ca2+ buffering and Ca2+ transport and regulation of various enzyme systems. They potentially have a number of different effects on cells includingaltering the duration of action potentials, promoting neuronal bursting activity and protecting cells against the damaging effects of excessive calcium influx. The present study has been designed to clarify the differential responding patterns of parvalbumin immunoreactive neurons in the rat retina following diabetic injury, for better understandings of role of parvalbumin in the retinal circuitry and in calcium homeostasis. Experimental diabetes was induced by a single intravenous injection of streptozotocin in a dose of 60 mg/kg body weight. Diabetic rats showing high blood glucose levels (above 300 mg/dL) were cared for 1, 4, 8, 12 and 24 weeks, respectively. The retinas at each time point were processed for immunohistochemistry and Western blotting using antiparvalbumin antibody. In the rat retina at normal, parvalbumin immunoreactivity appeared in AII amacrine cells, amacrine cells of a widefield type and displaced amacrine cells. A few bipolar cells are also showed the reactivity. During diabetes, the intensity of parvalbumin immunoreactivity is decreased especially in the AII amacrine cells. The cell number of parvalbumin immunoreactive neurons has showed no large changes throughout the diabetes, except that of bipolar cells. That population of parv immunoreactive of bipolar cells has increased remarkably at later diabetic periods. The protein levels of parvalbumin have showed transiently a slight increase at earlier diabetic periods, and then decreased to lower than that of normal. Parvalbumin immunoreactive bipolar cells at diabetes are co-localized not with PKC-alpha or recoverin, but with glutamate transporter Glt-1b. AII amacrine cell processes were joined with each other and with axon terminals of presumed cone bipolar cells by gap junction. These results suggest that the calcium buffering activity of parvalbumin is shifted from AII amacrine cells to a certain type of cone bipolar cells, in response to diabetes. This event may be occurred through electrically coupled gap junction in between these cell processes.