AT1 receptors and L-type calcium channels: functional coupling in supersensitivity to angiotensin II in diabetic rats

Cardiovasc Res. 2005 Feb 1;65(2):374-86. doi: 10.1016/j.cardiores.2004.10.010.


Objective: The study was designed to investigate the role of calcium channels in enhanced angiotensin II (Ang II)-induced contraction in thoracic aortic rings from diabetic rats.

Methods: Ang II-induced isometric tension was studied in thoracic aortic rings isolated from control or streptozotocin-induced (8 weeks) diabetic rats. Saturation binding studies at AT1 receptors and L-type calcium channels were performed using [3H] Ang II and [3H] PN200110, respectively. Ang II-induced calcium influx was studied in fura-2-loaded single vascular smooth muscle cells isolated from thoracic aorta of control and diabetic rats.

Results: Ang II did not induce contraction in calcium-free Krebs. In the presence of extracellular calcium, increased Emax (mg/mm2) and pD2 to Ang II was observed in aortic rings from diabetic (795.54+/-38.19; 8.27+/-0.12) compared to control (230.09+/-25.45; 7.68+/-0.22) rats, respectively. Nimodipine but not verapamil or diltiazem dose-dependently blocked the Ang II-induced contractions in a noncompetitive manner and its -log IC50 was significantly lower in aortic rings from diabetic (8.81+/-0.10) compared to control (9.34+/-0.11) rats. The Ang II-induced increase in intracellular calcium levels was significantly enhanced (2.5-fold) in vascular smooth muscle cells from diabetic rats. AT1 receptor saturation binding with [3H] Ang II revealed a significantly higher affinity (nM) and Bmax (pmol/mg protein) in aortic vascular membrane preparation from diabetic (0.31+/-0.04; 64.18+/-2.4) compared to control (0.52+/-0.02; 47.81+/-2.8) rats, respectively, while L-type calcium channel saturation binding with [3H] PN200110 showed a higher affinity (nM) with no change in the Bmax (fmol/mg protein) in diabetic (0.74+/-0.08; 4.52+/-0.40) compared to control (1.49+/-0.32; 5.43+/-0.60) aortic membranes, respectively.

Conclusions: Our results suggest that Ang II-induced contraction is dependent on extracellular calcium, and enhanced functional coupling of AT1 receptors and DHP-sensitive L-type calcium channels results in supersensitivity to Ang II in thoracic aorta isolated from diabetic rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiotensin II / pharmacology*
  • Animals
  • Aorta, Thoracic
  • Calcium / analysis
  • Calcium / metabolism
  • Calcium / pharmacology
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels, L-Type / metabolism*
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Depression, Chemical
  • Diabetes Mellitus, Experimental / metabolism*
  • Dose-Response Relationship, Drug
  • In Vitro Techniques
  • Isradipine / pharmacology
  • Male
  • Muscle Contraction / drug effects
  • Muscle, Smooth, Vascular / drug effects
  • Muscle, Smooth, Vascular / metabolism*
  • Nimodipine / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Receptor, Angiotensin, Type 1 / metabolism*


  • Calcium Channel Blockers
  • Calcium Channels, L-Type
  • Receptor, Angiotensin, Type 1
  • Angiotensin II
  • Nimodipine
  • Calcium
  • Isradipine