Purpose: To investigate the effect of electrical stimulation (ES) on the induction of insulin-like growth factor 1 (IGF-1) in cultured retinal Müller cells.
Methods: Müller cells were isolated from rat retinas. ES was applied to Müller 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 ([Ca(2+)]) induced by ES was monitored by Ca(2+) imaging with Fura 2-AM. Ca(2+) imaging and RT-PCR were performed with and without the application of l muM 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. [Ca(2+)] 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 Ca(2+) influx were suppressed by nifedipine.
Conclusions: These results indicate that the enhancement of IGF-1 transcription by ES in cultured Müller cells depends largely on Ca(2+) influx through L-type Ca(2+) channels.