| First Author | Lu M | Year | 2004 |
| Journal | Am J Physiol Renal Physiol | Volume | 286 |
| Issue | 3 | Pages | F490-5 |
| PubMed ID | 14600033 | Mgi Jnum | J:95434 |
| Mgi Id | MGI:3525983 | Doi | 10.1152/ajprenal.00305.2003 |
| Citation | Lu M, et al. (2004) ROMK is required for expression of the 70-pS K channel in the thick ascending limb. Am J Physiol Renal Physiol 286(3):F490-5 |
| abstractText | Apical potassium recycling is crucial for salt transport by the thick ascending limb (TAL). Loss-of-function mutations in the K channel, ROMK (Kir1.1; KCNJ1), cause Bartter syndrome, a genetically heterogeneous disorder characterized by severe reduction in salt absorption by the TAL, Na wasting, polyuria, and hypokalemic alkalosis. ROMK(-/-) null mice exhibit a Bartter phenotype and lack the small-conductance (30-pS) apical K channel (SK) in the TAL. However, a distinct 70-pS K channel can also significantly contribute to the apical conductance of TAL. We now examine the effect of ROMK deletion on the functional expression of the 70-pS K channel in the TAL. Functional expression of the 70-pS K channel was low [average channel activity (NP(o)) = 0.02] in ROMK(+/+) mice on a control K diet but increased to 0.27 by high-K intake for 2 wk. In contrast, the high-K diet decreased NP(o) of SK by approximately 30%, from 2.04 to 1.44. In ROMK heterozygous (+/-) mice on a control K diet, SK activity was about one-half of that observed in ROMK(+/+) mice (0.95 vs. 2.04). The high-K diet also reduced SK activity in ROMK(+/-) mice by approximately 40% (from 0.95 to 0.55) but increased NP(o) of the 70-pS K channel from 0 to 0.09 in ROMK(+/-) mice. This corresponds to approximately 30% of channel activity (NP(o) = 0.27) observed in ROMK(+/+) mice. Neither the 70-pS nor the 30-pS K channels were observed in TAL cells from ROMK(-/-) mice on either the normal or high-K diets. Thus functional expression of the 70-pS K channel is enhanced by increasing dietary K and requires expression of ROMK. It is likely that ROMK forms a critical subunit of the 70-pS K channel, accounting for the loss of apical K secretory channel activity in ROMK Bartter syndrome. |
