Basolateral pH-Sensitive K+ Channels Mediate Membrane Potential of Proximal Tubule Cells in Bullfrog Kidney.

Kubokawa, Masaru; Mori, Yoshiaki; Fujimoto, Katsuhisa; Kubota, Takeshi

doi:10.2170/jjphysiol.48.1

Cited by 5 publications

(1 citation statement)

References 28 publications

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Ca2+-Dependent Inhibition of Inwardly Rectifying K+ channel in Opossum Kidney Cells.

Mori

Kawasaki²,

Takamaki³

et al. 2001

JJP

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It has been demonstrated in both mammalian and amphibian proximal tubule cells with the patch-clamp and microelectrode techniques that the inwardly rectifying pH-sensitive and ATP-regulated K ϩ channel with a conductance of about 50 pS mediate the membrane potential of proximal tubule cells [1][2][3]. We have demonstrated that in cultured opossum kidney proximal tubule (OKP) cells, the inwardly rectifying pH-sensitive K ϩ channel with a conductance of about 70-90 pS is regulated by ATP, protein kinase A (PKA), and inhibited by Ba 2ϩ or glybenclamide, a specific inhibitor of sulfonylurea receptor [4][5][6]. Besides electrophysiological studies, the cloning and reconstitution studies demonstrated that ATP-sensitive K ϩ channels are heteromultimers of inwardly rectifying K ϩ channel subunits (Kir6.x) and sulfonylurea receptors (SUR) [7]. Moreover, it has also been indicated with the histochemical studies of the inwardly rectifying ATP-sensitive K ϩ channel (Kir6.1) that Kir6.1 with a conductance of 70 pS is ubiquitously Japanese Journal of Physiology, 51, 371-380, 2001 Key words: proximal tubule cell, inwardly rectifying K ؉ channel, PKC, CaMK II, calcineurin. Abstract:The effect of intracellular Ca 2ϩ on the activity of the inwardly rectifying ATP-regulated K ϩ channel with an inward conductance of about 90 pS was examined by using the patchclamp technique in opossum kidney proximal tubule (OKP) cells. The activity of the inwardly rectifying K ϩ channel rapidly declined with an application of ionomycin (1 M) in the presence of 10 Ϫ6 M Ca 2ϩ in cell-attached patches. The application of 10 M phorbor-12-myristate-acetate (PMA) with 10 Ϫ6 M Ca 2ϩ reduced the K ϩ channel activity. Although the channel activity was not influenced by an increase of bath Ca 2ϩ from 10 Ϫ7.5to 10 Ϫ6 M, the activity was inhibited by protein kinase C (PKC, 1 U/ml) with 10 Ϫ6 M Ca 2ϩ in insideout patches. The inhibitory effect of Ca 2ϩ with ionomycin on the channel activity was diminished by the pretreatment with a specific PKC inhibitor, GF 109203X (5 M), in cell-attached patches. By contrast, the application of Ca 2ϩ /calmodulin kinase II (CaMK II, 300 pM) dramatically increased this channel activity in inside-out patches. In cellattached patches, the addition of both GF 109203X and cyclospolin A (5 M), a potent inhibitor of protein phosphatase 2B (calcineurin), instead stimulated the K ϩ channel activity with ionomycin and 10 Ϫ6 M Ca 2ϩ. The addition of protein phosphatase 2B (calcineurin) (2 U/ml) to the bath with calmodulin (1 M) and Ni 2ϩ (10 M) to stimulate calcineurin inhibited the channel activity in inside-out patches. Furthermore, the inhibitory effect of PKC or calcineurin on this channel activity was abolished by a removal of Ca

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