Involvement of calcium-activated potassium channels in the regulation of DNA synthesis in cultured Müller glial cells.
OBJECTIVE
To determine the involvement of Ca(2+)-activated K(+) channels of big conductance (BK) and of Ca(2+) channels in the regulation of DNA synthesis in cultured guinea pig Müller cells. DNA synthesis was stimulated by elevated extracellular potassium, by serum, or by epidermal growth factor.


METHODS
Dissociated retinas from guinea pigs were cultured for 8 days. Just before confluence was achieved, the cultures were treated with the test substances in serum-free or serum-containing media. The rates of DNA synthesis were assessed by a quantitative bromodeoxyuridine immunoassay. The intracellular Ca(2+) concentration was measured by the fura-2 fluorescence technique.


RESULTS
Blocking the BK channels with tetraethylammonium or by iberiotoxin had no effect at normal extracellular K(+) (5.8 mM) but decreased the rate of DNA synthesis at higher extracellular K(+) (10 or 25 mM). Epidermal growth factor-induced DNA synthesis was decreased by block of BK channels or by application of the Ca(2+) channel blockers nimodipine and flunarizine. Application of epidermal growth factor elevated the intracellular Ca(2+) concentration of cultured Müller cells. This elevation was diminished by co-application of iberiotoxin or of flunarizine.


CONCLUSIONS
The activity of BK channels is necessary for elevated DNA synthesis in Müller cells when their membranes are depolarized and/or when the Ca(2+) influx into Müller cells is increased by growth factors. BK channels may contribute to the maintenance of DNA synthesis by increasing mitogen-induced increase in intracellular Ca(2+) concentration.
Kodal
H
H
Department of Neurophysiology, Paul Flechsig Institute of Brain Research, University of Leipzig, Germany.
Weick
M
M
Moll
V
V
Biedermann
B
B
Reichenbach
A
A
Bringmann
A
A
D000818:Animals; D001769:Blood; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004261:DNA Replication / Q000187:drug effects; D004594:Electrophysiology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D016257:Fura-2 / Q000378:metabolism; D006168:Guinea Pigs; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials; D009457:Neuroglia / Q000166:cytology / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D019789:Tetraethylammonium / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D004815:Epidermal Growth Factor; D019789:Tetraethylammonium; C064719:iberiotoxin; D004247:DNA; D011188:Potassium; D002118:Calcium; D016257:Fura-2