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Notes
      3. Old stuff
          3.2. Old physio stuff (around 2005)
              3.2.3. Physiology
                  3.2.3.2. Cardiovascular
                      3.2.3.2.2. Heart
                          3.2.3.2.2.2. Electrical activity
                              3.2.3.2.2.2.2. Fast-response cardiac action potential
 3.2.3.2.2.2.2.2. Calcium channel 

Calcium channel

Types of Ca2+ channels (L and T)

L-type Ca2+ channels

Activated when Vm is about -30 to -40mV [WG21:p80]

--> L-type channel activates (slower than fast Na+ channel)

--> Inward Ca2+ current

--> Inactivates very slowly

Other points about L-type Ca2+ channel
  • Prominent in heart
  • Activated when MP reached about -10mV during phase 0
  • Blocked by Ca2+ channel blockers
    e.g. verapamil, nifedipine, and diltiazem
  • Catecholamines interact with beta-adrenergic receptors
    --> activating adenylyl cyclase
    --> increasing cAMP
    --> enhance activation of L-type Ca2+ channel
  • The channel protein is called dihydropyridine receptor
    * [BL8:p62]

T-type Ca2+ channels

Produced when Vm changes from -80 to -20mV

  • Involved in production of pacemaker potential
  • Minimally (?? or not at all) affected by catecholamines
  • Fast activation, fast deactivation
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