Introduction

• Vascular Endothelium


  Metabolism, Vascular Tone
• Vasoconstrictors (Endothelin)


  Promote depolarization, elevate calcium
• Vasodilators (NO/PGI2, EDHF)


  Promote hyperpolarization, reduce calcium
• Endothelin


  Kinase C Pathway
• NO 


  Closure of calcium channels
• PGI2 


  Inhibit myosin light chain kinase
• EDHF (Gap junctions)


  Open potassium channels
• KCa


  SK/IK (Micro regulation, calcium as regulator and will not inactivate at negative membrane potential), BK (Voltage-dependent, absent in hyperpolarization)
• KCa


  Couple changes in calcium to hyperpolarization
• SK3/IK


  SK abundant in endothelia
• TRAM-34, TRAM-39


  Abolish IK potassium current
• TRAM-34, TRAM-39 + SK3 Inhibitor


  Block NO
• NS309


  Lower calcium
• Deletion of IK/SK3 genes

  Impaired hyperpolarization
• Doxycycline


  Lowers potassium
• Overexpression of SK3


  Increases potassium
• Acetylcholine, bradykinin, substance P (Agonists)


  Release calcium into cytosol, induce synthesis of EDHF
• Acetylcholine


  Stimulates NO synthase, NON-EDHF vasodilation, elevates calcium
• Bradykinin


  Intracellular calcium release, NO synthase stimulation, NON-EDHF vasodilation
• Substance P 


  Calcium influx
• Elevated intracellular calcium, EDHF synthesis


  Stimulate KCa, calcium-induced opening of SK/IK for endothelial hyperpolarization
• SK/IK 


  Potassium efflux, muscle contraction
• EDHF


  Could be potassium
• EDHF-SK/IK vasodilation 


  Inhibited by NO
• NS309 (IK activator)


  Hyperpolarization
• Protein kinase C (requires calmodulin) 


  SK inhibition by reducing calcium sensitivity
• Degree of endothelial dysfunction

  Ability to dilate or constrict in response to drug
• Diabetes


  Increased endothelial constriction, hampered vasorelaxation
• Variation across studies


  Different time points
• Diabetic 


  Decreased SK currents and responsiveness to EDHF
• Post translational


  Lack of changes in SK
• Highfat (Mesenteric artery)


  Unregulated IK
• Highfat, high fructose (Mesenteric artery)


  Downregulated SK and IK
• Cafeteria (Saphenous artery)


  Relaxation preserved
• Importance to study coronary artery dysfunction

  It is more severe in diabetics
• Diabetes


  Increase NADH (Decrease SK/BK), increase NADH/NAD+ ratio (decrease sodium for cardiac impulse)
• NADH 


  Facilitates diabetic inhibition of SK channels
• ROS inhibition (mitochondria)


  Relaxation improved, increased SK
• Hyperglycemia


  Increases protein kinase C and DAG
• Protein kinase C


  Increases vasoconstrictors, reduces gap junction signaling