Properties of a Ca(2+)-activated large conductance K(+) channel with ATP sensitivity in human renal proximal tubule cells.
The properties of a native Ca(2+)-activated large conductance K(+) channel (BK channel) present in the surface membrane of cultured human renal proximal tubule epithelial cells (RPTECs) were investigated by using the patch-clamp technique. The slope conductance of the BK channel was about 295 pS, and the channel was selective to K(+) over Na(+), with a selectivity ratio of about 12.2. The activity of the channel was almost maximally enhanced by 10(-4 )M or more Ca(2+) in the cytoplasmic surface of the patch membrane and was markedly diminished by reducing the cytoplasmic Ca(2+) to 10(-6) M at the membrane potential of about 0 mV. The depolarization of the patch membrane also enhanced the channel activity, and hyperpolarization lowered it. K(+) channel blockers, Ba(2+) (0.1-1 mM), tetraethylammonium (1 mM), and charybdotoxin (100 nM), were effective for the suppression of channel activity. A significant feature of the K(+) channel was that channel activity maintained by 10(-5)-10(-4 )M Ca(2+) in inside-out patches was inhibited by the addition of ATP (1-10 mM) to the bath solution. ATPgammaS, and a nonhydrolyzable ATP analogue, 5'-adenylylimidodiphosphate (AMP-PNP), also had inhibitory effects on channel activity. However, an inhibitor of ATP-sensitive K(+) channels, glibenclamide (0.1 mM), induced no appreciable change in channel activity from both intra- and extracellular sides. These results suggest that besides the common natures of the BK channel family such as regulation by cytoplasmic Ca(2+) and membrane potential, the BK channel in RPTECs is directly inhibited by intracellular ATP independent of phosphorylation processes and sulfonylurea receptor.
Hirano
J
J
Department of Physiology II, School of Medicine, Iwate Medical University, Morioka, 020-8505, Japan. jhirano@iwate-med.ac.jp
Nakamura
K
K
Kubokawa
M
M
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism*; D002118:Calcium / Q000493:pharmacokinetics*; D018929:Cell Culture Techniques; D003593:Cytoplasm / Q000737:chemistry; D004847:Epithelial Cells / Q000502:physiology; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000502:physiology*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug / Q000502:physiology; D064233:Sulfonylurea Receptors
D018528:ATP-Binding Cassette Transporters; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000255:Adenosine Triphosphate; D002118:Calcium