Spatial distribution of spermine/spermidine content and K+-current rectification in frog retinal glial (Müller) cells
✍ Scribed by Serguei N. Skatchkov; Misty J. Eaton; Jan Krušek; Rüdiger W. Veh; Bernd Biedermann; Andreas Bringmann; Thomas Pannicke; Richard K. Orkand; Andreas Reichenbach
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 157 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0894-1491
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✦ Synopsis
Previous studies in retinal glial (Mu ¨ller) cells have suggested that (1) the dominant membrane currents are mediated by K ϩ inward-rectifier (Kir) channels (Newman and Reichenbach, Trends Neurosci 19:307-312, 1996), and (2) rectification of these Kir channels is due largely to a block of outward currents by endogenous polyamines such as spermine/spermidine (SPM/SPD) (Lopatin et al., Nature 372:366 -369, 1994). In frog Mu ¨ller cells, the degree of rectification of Kir-mediated currents is significantly higher in the endfoot than in the somatic membrane (Skatchkov et al., Glia 27:171-181, 1999). This article shows that in these cells there is a topographical correlation between the local cytoplasmic SPM/SPD immunoreactivity and the ratio of inward to outward K ϩ currents through the surrounding membrane area. Throughout the retina, Mu ¨ller cell endfeet display a high SPM/SPD immunolabel (assessed by densitometry) and a large inward rectification of K ϩ currents, as measured by the ratio of inward to outward current produced by step changes in [K ϩ ] o . In the retinal periphery, Mu ¨ller cell somata are characterized by roughly one-half of the SPM/SPD immunoreactivity and K ϩ -current rectification as the corresponding endfeet. In the retinal center, Mu ¨ller cell somata are virtually devoid of both SPM/SPD immunolabel and K ϩ -current inward rectification. Comparing one region of the retina with another, we find an exponential correlation between the local K ϩ rectification and the local SPM/SPD content. This finding suggests that the degree of inward rectification in a given membrane area is determined by the local cytoplasmic polyamine concentration. GLIA 31: 84 -90, 2000.