Spatial distribution of spermine/spermidine content and K(+)-current rectification in frog retinal glial (Müller) cells.
Previous studies in retinal glial (Müller) cells have suggested that (1) the dominant membrane currents are mediated by K(+) 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 Müller 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(+) currents through the surrounding membrane area. Throughout the retina, Müller cell endfeet display a high SPM/SPD immunolabel (assessed by densitometry) and a large inward rectification of K(+) currents, as measured by the ratio of inward to outward current produced by step changes in [K(+)](o). In the retinal periphery, Müller cell somata are characterized by roughly one-half of the SPM/SPD immunoreactivity and K(+)-current rectification as the corresponding endfeet. In the retinal center, Müller cell somata are virtually devoid of both SPM/SPD immunolabel and K(+)-current inward rectification. Comparing one region of the retina with another, we find an exponential correlation between the local K(+) 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.
Skatchkov
S N
SN
CMBN, Department of Biochemistry, School of Medicine, Universidad Central del Caribe, Bayamon, Puerto Rico.
Eaton
M J
MJ
Krusek
J
J
Veh
R W
RW
Biedermann
B
B
Bringmann
A
A
Pannicke
T
T
Orkand
R K
RK
Reichenbach
A
A
D000818:Animals; D004553:Electric Conductivity; D004594:Electrophysiology; D007150:Immunohistochemistry / Q000379:methods; D009457:Neuroglia / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D011894:Rana pipiens; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D013095:Spermidine / Q000378:metabolism*; D013096:Spermine / Q000378:metabolism*; D013194:Staining and Labeling; D014018:Tissue Distribution
D015221:Potassium Channels; D013096:Spermine; D013095:Spermidine