Ontogeny of flow-stimulated potassium secretion in rabbit cortical collecting duct: functional and molecular aspects.
High urinary flow rates stimulate K secretion in the fully differentiated but not neonatal or weanling rabbit cortical collecting duct (CCD). Both small-conductance secretory K and high-conductance Ca2+/stretch-activated maxi-K channels have been identified in the apical membrane of the mature CCD by patch-clamp analysis. We reported that flow-stimulated net K secretion in the adult rabbit CCD is 1) blocked by TEA and charybdotoxin, inhibitors of intermediate- and high-conductance (maxi-K) Ca2+-activated K channels, and 2) associated with increases in net Na absorption and intracellular Ca2+ concentration ([Ca2+]i). The present study examined whether the absence of flow-stimulated K secretion early in life is due to a 1) limited flow-induced rise in net Na absorption and/or [Ca2+]i and/or 2) paucity of apical maxi-K channels. An approximately sixfold increase in tubular fluid flow rate in CCDs isolated from 4-wk-old rabbits and microperfused in vitro led to an increase in net Na absorption and [Ca2+]i, similar in magnitude to the response observed in 6-wk-old tubules, but it failed to generate an increase in net K secretion. By 5 wk of age, there was a small, but significant, flow-stimulated rise in net K secretion that increased further by 6 wk of life. Luminal perfusion with iberiotoxin blocked the flow stimulation of net K secretion in the adult CCD, confirming the identity of the maxi-K channel in this response. Maxi-K channel alpha-subunit message was consistently detected in single CCDs from animals >/=4 wk of age by RT-PCR. Indirect immunofluorescence microscopy using antibodies directed against the alpha-subunit revealed apical labeling of intercalated cells in cryosections from animals >/=5 wk of age; principal cell labeling was generally intracellular and punctate. We speculate that the postnatal appearance of flow-dependent K secretion is determined by the transcriptional/translational regulation of expression of maxi-K channels. Furthermore, our studies suggest a novel function for intercalated cells in mediating flow-stimulated K secretion.
Woda
Craig B
CB
Department of Pediatrics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Miyawaki
Nobuyuki
N
Ramalakshmi
Santhanam
S
Ramkumar
Mohan
M
Rojas
Raul
R
Zavilowitz
Beth
B
Kleyman
Thomas R
TR
Satlin
Lisa M
LM
D000042:Absorption; D000375:Aging / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007672:Kidney Cortex; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009994:Osmolar Concentration; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D012079:Renal Circulation / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D014018:Tissue Distribution
D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D012333:RNA, Messenger; C064719:iberiotoxin; D012964:Sodium; D011188:Potassium; D002118:Calcium