Abstract
Purpose::
In vivo experiments have shown that the electrical stimulation (ES) of the rat retina up-regulates the production of insulin-like growth factor-1 (IGF-1), and immunohistochemical studies suggested that the Muller cells were involved in this increase (Morimoto T, et al. IOVS, 2005). The purpose of this study was to investigate the effect of ES on cultured rat retinal Muller cells.
Methods::
Primary Muller cells were obtained from Long-Evans rats at postnatal day 12 to 14 as described (Hicks D, et al. Exp Eye Res, 1990). ES was applied to one-passaged Muller cells with biphasic pulses (duration, 1 ms; current, 0-10mA; frequency, 20Hz) for 30 min. The mRNA level of IGF-1 was determined by RT-PCR immediately, 1 hour, and 2 hours after ES (n=12). The intracellular calcium concentration was determined by calcium imaging (Ca2+ imaging) with Fura-2 with and without Nifedipine (L-type calcium channel blocker) before to 2 hours after ES (n=11).
Results::
RT-PCR showed a significant increase (P<0.05) of IGF-1 with a current of 10mA compared with that of 0mA just after the cessation of ES. Ca2+ imaging demonstrated that the intracellular calcium concentration began to increase immediately after the beginning of ES, reached a maximum of 1.5 fold at 30 min, and continued to increase until about 15 min after the cessation of ES. This calcium influx was completely blocked by Nifedipine.
Conclusions::
The ES induced IGF-1 transcription, and the intracellular calcium influx via L-type calcium channel had similar time course in cultured Muller cells. These results suggest that the calcium influx triggered by ES may be related to the transcription of IGF-1.
Keywords: retinal glia • neuroprotection • ion channels