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Ionic transport in macula densa cells

J Y Lapointe1, A Laamarti, P D Bell

  • 1Groupe de recherche en transport membranaire, Département de Physique, Université de Montréal, Canada. lapoinj@ere.umontreal.ca

Kidney International. Supplement
|September 15, 1998
PubMed
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Macula densa (MD) cells utilize a furosemide-sensitive Na:K:2Cl cotransporter, influencing intracellular ion concentrations. This study reveals MD cells have significant transport activity, contrary to previous assumptions.

Area of Science:

  • Renal physiology
  • Cellular transport mechanisms

Background:

  • Macula densa (MD) cells play a crucial role in kidney function.
  • Previous understanding suggested limited transport activity in MD cells.

Purpose of the Study:

  • To investigate the functional characteristics and transport properties of macula densa (MD) cells.
  • To determine the impact of luminal NaCl concentration on intracellular ion homeostasis in MD cells.

Main Methods:

  • Microelectrode and patch-clamp electrophysiology on rabbit isolated thick ascending limb (TAL)/glomerulus preparations.
  • Intracellular pH (pHi) measurements and thermodynamic considerations for ion concentration estimation.
  • Analysis of furosemide-sensitive transport and ammonium (NH4+) flux.

Main Results:

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  • MD cells possess a furosemide-sensitive Na:K:2Cl cotransporter, apical K+ channel, and basolateral Cl- conductance.
  • Luminal NaCl increases intracellular chloride, stimulating basolateral efflux and causing depolarization.
  • Intracellular Na+ and Cl- concentrations vary significantly with cotransporter activity, ranging from 6-7 mM to 70 mM and 20 mM, respectively.
  • Apical NH4+ transport influences pHi and indicates substantial transport activity in MD cells, comparable to TAL cells.

Conclusions:

  • MD cells exhibit significant transport activity, challenging prior notions of low transport capacity.
  • Intracellular ion concentrations in MD cells are dynamically regulated by luminal NaCl levels via the Na:K:2Cl cotransporter.
  • The findings provide new insights into the physiological mechanisms governing renal salt and water balance.