Cell-specific expression of amiloride-sensitive, Na(+)-conducting ion channels in the kidney.
Amiloride-sensitive, electrogenic Na+ absorption across the distal nephron plays a vital role in regulating extracellular fluid volume and blood pressure. Recently, two amiloride-sensitive, Na(+)-conducting ion channel cDNAs were cloned. One, an epithelial Na(+)-selective channel (ENaC), is responsible for Na+ absorption throughout the distal nephron. The second, a guanosine 3',5'-cyclic monophosphate (cGMP)-inhibitable cation channel, is conductive to Na+ and Ca2+ and contributes to Na+ absorption across the inner medullary collecting duct (IMCD). As a first step toward understanding the segment-specific contributions(s) of cGMP-gated cation channels and ENaC to Na+ and Ca2+ uptake along the nephron, we used in situ reverse transcription-polymerase chain reaction (RT-PCR) hybridization, solution-phase RT-PCR, and Western blot analysis to examine the nephron and cell-specific expression of these channels in mouse kidney cell lines and/or dissected nephron segments. cGMP-gated cation channel mRNA was detected in proximal tubule, medullary thick ascending limb (mTAL), distal convoluted tubule (DCT), cortical collecting duct (CCD), outer medullary collecting duct (OMCD), and IMCD. cGMP-gated cation channel protein was detected in DCT, CCD, and IMCD cell lines. These observations suggest that hormones that modulate intracellular cGMP levels may regulate Na+, and perhaps Ca2+, uptake throughout the nephron. mRNA for alpha-mENaC, a subunit of the mouse ENaC, was detected in mTAL, DCT, CCD, OMCD, and IMCD. Coexpression of alpha-mENaC and cGMP-gated cation channel mRNAs in mTAL, DCT, CCD, OMCD, and IMCD suggests that both channels may contribute to Na+ absorption in these nephron segments.
Ciampolillo
F
F
Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
McCoy
D E
DE
Green
R B
RB
Karlson
K H
KH
Dagenais
A
A
Molday
R S
RS
Stanton
B A
BA
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D015870:Gene Expression; D017403:In Situ Hybridization; D015640:Ion Channel Gating / Q000187:drug effects; D007668:Kidney / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000235:genetics*
D012333:RNA, Messenger; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D000584:Amiloride