Effect of electrical stimulation on IGF-1 transcription by L-type calcium channels in cultured retinal Muller cells

Purpose: To investigate the effect of electrical stimulation (ES) on the induction of insulin-like growth factor 1 (IGF-1) in cultured retinal Muller cells. Methods: Muller cells were isolated from rat retinas. ES was applied to Muller cells of passage 1 with biphasic pulses (duration, 1 ms; frequency, 20 Hz; current, 0-10 mA) for 30 min. The mRNA level of IGF-1 was determined by reverse transcription-polymerase chain reaction (RT-PCR) immediately to 2 h after ES. The change of intracellular calcium concentration ([Ca2+]) induced by ES was monitored by Ca2+ imaging with Fura 2-AM. Ca2+ imaging and RT-PCR were performed with and without the application of l mu M nifedipine, an L-type calcium channel blocker. Results: The mRNA level of IGF-1 was increased significantly (P < 0.05) by about 1.3-fold immediately after 10 mA ES. [Ca2+] began to increase immediately after the start of ES, reached a maximum of approximately 1.8-fold, and continued to increase until about 20 min after the ES. The inductions of IGF-1 transcription and Ca2+ influx were suppressed by nifedipine. Conclusions: These results indicate that the enhancement of IGF-1 transcription by ES in cultured Muller cells depends largely on Ca2+ influx through L-type Ca2+ channels.