Insulin exits skeletal muscle capillaries by fluid-phase transport

J Clin Invest. 2018 Feb 1;128(2):699-714. doi: 10.1172/JCI94053. Epub 2018 Jan 8.


Before insulin can stimulate myocytes to take up glucose, it must first move from the circulation to the interstitial space. The continuous endothelium of skeletal muscle (SkM) capillaries restricts insulin's access to myocytes. The mechanism by which insulin crosses this continuous endothelium is critical to understand insulin action and insulin resistance; however, methodological obstacles have limited understanding of endothelial insulin transport in vivo. Here, we present an intravital microscopy technique to measure the rate of insulin efflux across the endothelium of SkM capillaries. This method involves development of a fully bioactive, fluorescent insulin probe, a gastrocnemius preparation for intravital microscopy, an automated vascular segmentation algorithm, and the use of mathematical models to estimate endothelial transport parameters. We combined direct visualization of insulin efflux from SkM capillaries with modeling of insulin efflux kinetics to identify fluid-phase transport as the major mode of transendothelial insulin efflux in mice. Model-independent experiments demonstrating that insulin movement is neither saturable nor affected by insulin receptor antagonism supported this result. Our finding that insulin enters the SkM interstitium by fluid-phase transport may have implications in the pathophysiology of SkM insulin resistance as well as in the treatment of diabetes with various insulin analogs.

Keywords: Insulin; Metabolism; Skeletal muscle; Vascular Biology; endothelial cells.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antigens, CD / metabolism
  • Biological Transport
  • Capillaries / metabolism*
  • Diabetes Mellitus / therapy
  • Glucose / metabolism
  • Glucose Clamp Technique
  • Humans
  • Hyperinsulinism
  • Image Processing, Computer-Assisted
  • Insulin / metabolism*
  • Intravital Microscopy
  • Kinetics
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Models, Theoretical
  • Muscle, Skeletal / blood supply*
  • Protein Binding
  • Receptor, Insulin / metabolism
  • Rhodamines / chemistry


  • Antigens, CD
  • Insulin
  • Rhodamines
  • INSR protein, human
  • Receptor, Insulin
  • Glucose