Functional expression of Kir 6.1/SUR1-K(ATP) channels in frog retinal Müller glial cells.
The retinae and brains of larval and adult amphibians survive long-lasting anoxia; this finding suggests the presence of functional K(ATP) channels. We have previously shown with immunocytochemistry studies that retinal glial (Müller) cells in adult frogs express the K(ATP) channel and receptor proteins, Kir6.1 and SUR1, while retinal neurons display Kir6.2 and SUR2A/B (Skatchkov et al., 2001a: NeuroReport 12:1437-1441; Eaton et al., in press: NeuroReport). Using both immunocytochemistry and electrophysiology, we demonstrate the expression of Kir6.1/SUR1 (K(ATP)) channels in adult frog and tadpole Müller cells. Using conditions favoring the activation of K(ATP) channels (i.e., ATP- and spermine-free cytoplasm-dialyzing solution containing gluconate) in Müller cells isolated from both adult frogs and tadpoles, we demonstrate the following. First, using the patch-clamp technique in whole-cell recordings, tolbutamide, a blocker of K(ATP) channels, blocks nearly 100% of the transient and about 30% of the steady-state inward currents and depolarizes the cell membrane by 5-12 mV. Second, inside-out membrane patches display a single-channel inward current induced by gluconate (40 mM) and blocked by ATP (200 microM) at the cytoplasmic side. The channels apparently show two sublevels (each of approximately 27-32 pS) with a total of 85-pS maximal conductance at -80 mV; the open probability follows a two-exponential mechanism. Thus, functional K(ATP) channels, composed of Kir6.1/SUR1, are present in frog Müller cells and contribute a significant part to the whole-cell K+ inward currents in the absence of ATP. Other inwardly rectifying channels, such as Kir4.1 or Kir2.1, may mediate the remaining currents. K(ATP) channels may help maintain glial cell functions during ATP deficiency.
Skatchkov
Serguei N
SN
CMBN, Department of Biochemistry, School of Medicine, Universidad Central del Caribe, Bayamón, Puerto Rico.
Rojas
Legier
L
Eaton
Misty J
MJ
Orkand
Richard K
RK
Biedermann
Bernd
B
Bringmann
Andreas
A
Pannicke
Thomas
T
Veh
Rüdiger W
RW
Reichenbach
Andreas
A
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000172:deficiency; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007150:Immunohistochemistry; D007814:Larva / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000378:metabolism*; D011892:Rana catesbeiana; D011894:Rana pipiens; D011898:Ranidae / Q000033:anatomy & histology / Q000254:growth & development / Q000378:metabolism*; D011955:Receptors, Drug; D012160:Retina / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D064233:Sulfonylurea Receptors; D014044:Tolbutamide / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D014665:Vasodilator Agents; D000255:Adenosine Triphosphate; D014044:Tolbutamide