Ca2+ dependence of flow-stimulated K secretion in the mammalian cortical collecting duct.
Apical low-conductance SK and high-conductance Ca(2+)-activated BK channels are present in distal nephron, including the cortical collecting duct (CCD). Flow-stimulated net K secretion (J(K)) in the CCD is 1) blocked by iberiotoxin, an inhibitor of BK but not SK channels, and 2) associated with an increase in [Ca(2+)](i), leading us to conclude that BK channels mediate flow-stimulated J(K). To examine the Ca(2+) dependence and sources of Ca(2+) contributing to flow-stimulated J(K), J(K) and net Na absorption (J(Na)) were measured at slow (approximately 1) and fast (approximately 5 nl.min(-1).mm(-1)) flow rates in rabbit CCDs microperfused in the absence of luminal Ca(2+) or after pretreatment with BAPTA-AM to chelate intracellular Ca(2+), 2-aminoethoxydiphenyl borate (2-APB), to inhibit the inositol 1,4,5-trisphosphate (IP(3)) receptor or thapsigargin to deplete internal stores. These treatments, which do not affect flow-stimulated J(Na) (Morimoto et al. Am J Physiol Renal Physiol 291: F663-F669, 2006), inhibited flow-stimulated J(K). Increases in [Ca(2+)](i) stimulate exocytosis. To test whether flow induces exocytic insertion of preformed BK channels into the apical membrane, CCDs were pretreated with 10 microM colchicine (COL) to disrupt microtubule function or 5 microg/ml brefeldin-A (BFA) to inhibit delivery of channels from the intracellular pool to the plasma membrane. Both agents inhibited flow-stimulated J(K) but not J(Na) (Morimoto et al. Am J Physiol Renal Physiol 291: F663-F669, 2006), although COL but not BFA also blocked the flow-induced [Ca(2+)](i) transient. We thus speculate that BK channel-mediated, flow-stimulated J(K) requires an increase in [Ca(2+)](i) due, in part, to luminal Ca(2+) entry and ER Ca(2+) release, microtubule integrity, and exocytic insertion of preformed channels into the apical membrane.
Liu
Wen
W
Department of Pediatrics, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1664, New York, NY 10029, USA.
Morimoto
Tetsuji
T
Woda
Craig
C
Kleyman
Thomas R
TR
Satlin
Lisa M
LM
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D020126:Brefeldin A / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002412:Cations / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006859:Hydrogen / Q000378:metabolism; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010477:Perfusion; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011817:Rabbits; D019284:Thapsigargin / Q000494:pharmacology
D001639:Bicarbonates; D002412:Cations; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010726:Phosphodiesterase Inhibitors; D011500:Protein Synthesis Inhibitors; D020126:Brefeldin A; D004533:Egtazic Acid; D019284:Thapsigargin; D006859:Hydrogen; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D011188:Potassium; D003078:Colchicine; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine