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