Regulation of M-like K+ current, IKx, by Ca (2+) -dependent phosphorylation in rod photoreceptors
Kurennyi, D.E.; Barnes, S.
American Journal of Physiology 272(6 Pt 1): C1844-C1853
1997
ISSN/ISBN: 0002-9513 PMID: 9227413 Document Number: 480560
An M-like K+ current (I-Kx) helps set the rod photoreceptor resting potential and accelerates the response to dim light. Recorded with ruptured-patch whole cell techniques, the amplitude of I-Kx diminished, and activation occurred at increasingly negative potentials as a function of time. In contrast, I-Kx was stable during nystatin perforated-patch recording. Stability during ruptured-patch recording could be induced by raising the intracellular Ca-2+ concentration ((Ca-2+)-i) or by including caffeine or D-myo-inositol 1,4,5-trisphosphate in the pipette. This Ca-2+-induced stability of I-Kx was blocked by inhibitors of Ca-2+/calmodulin-dependent protein kinases, such as W-7, KN-62, chelerythrine, or H-7. Okadaic acid, an inhibitor of protein phosphatases, maintained I-Kx. stability even at low (Ca-2+)-i. The requirement for phosphorylation was demonstrated by depleting MgATP or by providing 5'-adenylylimidophosphate, a nonhydrolyzable analog of ATP, either of which blocked the Ca-2+-induced stability of I-Kx. These observations show that phosphorylation regulates I-Kx and that a stimulus controlling this action is (Ca-2+)-i. Should (Ca-2+)-i change during light adaptation, changes in I-Kx might alter the resting potential and temporal response properties of rod photoreceptors.