Cytosolic [Ca2+] signaling pathway in macula densa cells

Am J Physiol. 1999 Sep;277(3):F472-6. doi: 10.1152/ajprenal.1999.277.3.F472.

Abstract

Previous micropuncture studies suggested that macula densa (MD) cells might detect variations in luminal sodium chloride concentration ([NaCl]l) through changes in cytosolic calcium ([Ca2+]c). To test this hypothesis, MD [Ca2+]c was measured with fluorescence microscopy using fura 2 in the isolated perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney. Tubules were bathed and perfused with a Ringer solution, [NaCl]l was varied and isosmotically replaced with N-methyl-D-glucamine cyclamate. Control [Ca2+]c, during perfusion with 25 mM NaCl and 150 mM NaCl in the bath, averaged 101. 6 +/- 8.2 nM (n = 21). Increasing [NaCl]l to 150 mM elevated [Ca2+]c by 39.1 +/- 5.2 nM (n = 21, P < 0.01). This effect was concentration dependent between zero and 60 mM [NaCl]l. The presence of either luminal furosemide or basolateral nifedipine or 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), a potent Cl- channel blocker, significantly reduced resting [Ca2+]c and abolished the increase in [Ca2+]c in response to increased [NaCl]l. Nifedipine failed to produce a similar inhibitory effect when added exclusively to the luminal perfusate. Also, 100 nM BAY K 8644, a voltage-gated Ca2+ channel agonist, added to the bathing solution increased [Ca2+]c by 33.2 +/- 8.1 nM (n = 5, P < 0.05). These observations suggest that MD cells may detect variations in [NaCl]l through a signaling pathway that includes Na+-2Cl--K+ cotransport, basolateral membrane depolarization via Cl- channels, and Ca2+ entry through voltage-gated Ca2+ channels.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium / physiology*
  • Cytosol / physiology
  • Fluorescent Dyes
  • Fura-2
  • Loop of Henle / physiology*
  • Rabbits
  • Signal Transduction*
  • Sodium Chloride / metabolism
  • Sodium Chloride / pharmacology

Substances

  • Fluorescent Dyes
  • Sodium Chloride
  • Calcium
  • Fura-2