Comparison of Skeletal Muscle Smooth Muscle and Cardiac Muscle

- Table 1-3 compares the ionic basis for the action potential and mechanism of contraction in skeletal muscle, smooth muscle, and cardiac muscle.

- Cardiac muscle is discussed in Chapter 3.

Table 1-3. Comparison of Skeletal, Smooth, and Cardiac Muscle

Feature

Skeletal Muscle

Smooth Muscle

Cardiac Muscle

Appearance

Striated

No striations

Striated

Upstroke of action

Inward Na+ current

Inward Na+ current

Inward Ca2+ current (SA

potential

(slow waves may

node)

bring membrane

Inward Na+ current (atria,

potential to

ventricles, Purkinje fibers)

threshold)

Plateau

No

No

No (SA node)

Yes (atria, ventricles,

Purkinje fibers; due to

inward Ca2t current)

Duration of action

~1 msec

-10 msec

150 msec (SA node, atria)

potential

250-300 msec (ventricles

and Purkinje fibers)

Excitation-

Action potential —» T

Action potential opens

Inward Ca2+ current during

contraction

tubules

voltage-gated Ca2+

plateau of action potential

coupling

Ca2+ released from

channels in cell

Ca2+-induced Ca2+ release

nearby SR

membrane

from SR

T [Ca21i

Hormones and

T [Ca2+li

transmitters open

IP3-gated Ca2+

channels in SR

Molecular basis for

Ca2+-troponin C

Ca2+-calmodulin

Ca2+-troponin C binding

contraction

binding

binding

T myosin light-chain

kinase

IP3 = inositol 1,4,5-triphosphate; SA = sinoatrial; SR = sarcoplasmic reticulum.

IP3 = inositol 1,4,5-triphosphate; SA = sinoatrial; SR = sarcoplasmic reticulum.

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