The second half of the distal tubule and the subsequent cortical collecting tubule have two distinct cell types:  principal cells and intercalated cells

TLS Online TPP Program

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#Unit 2. Cellular Organization

When the Ca2+ level rises, Ca2+ binds CaM.

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#Unit 2. Cellular Organization

The CaM*-Ca2+ complex binds and activates MLC kinase, phosphorylates the myosin LC. 

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#Unit 2. Cellular Organization

Phosphorylation of MLC 

unfolds the myosin II, active and can assemble into bipolar filaments for contraction

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#Unit 2. Cellular Organization

When the Ca2+ levels drop:

Myosin LC is dephosphorylated by MLC phosphatase, causing muscle relaxation.

TLS Online TPP Program

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#Unit 2. Cellular Organization

Sarcomere

Within each skeletal muscle cell are many myofibrils consisting of a repeating array of a specialized structure

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#Unit 2. Cellular Organization

Each sarcomere contains two major types of filaments: 

Thick filaments (myosin II)

Thin filaments (actin and associated proteins)