Three types of Smad proteins function in the TGF-β signaling pathway: 

R-Smads (Smad2 and Smad3)

Co-Smads (Smad4)

I-Smads (Smad7)

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#Id: 6535

#Unit 7. System Physiology – Animal

The binding of ATP to  ATP sensitive K+ channels in the β cells closes the channels, reducing the efflux of K+ ions from the cell. The resulting small depolarization of the plasma membrane

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#Id: 6536

#Unit 7. System Physiology – Animal

Small depolarization of the plasma membrane triggers the opening of voltage- sensitive Ca2+ channels

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#Id: 6537

#Unit 7. System Physiology – Animal

The influx of Ca2+ ions raises, triggering the fusion of insulin- containing secretory vesicles with the plasma membrane and the secretion of insulin

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#Id: 6538

#Unit 7. System Physiology – Animal

The insulin receptor, a receptor tyrosine kinase, activates several signal transduction pathways, including the one leading to the activation of protein kinase B

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#Id: 6539

#Unit 7. System Physiology – Animal

The insulin receptor is a combination of four subunits held together by disulfide linkages: 

Two alpha subunits 

Two beta subunits

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#Id: 6540

#Unit 7. System Physiology – Animal

The binding of insulin is communicated through the single TM helix of each beta subunit to the paired Tyr kinase domains inside the cell, activating them to phosphorylate each other on three Tyr residues (Tyr1158, Tyr1162, Tyr1163)