Cardiac Muscle, Dr. D. Penney

Table 2. Pacemaker (S-A nodal & A-V nodal) ion channel events: sodium and calcium gate opening / closing (slow conduction: <0.05-0.1 m./sec.).

State TMP Na+a (m) Na+i (h) Ca++a (d) Ca++i (f)
Resting state: -60 mv closed closed closed open
Depolarization: Activation 2 (Ca++ influx --> slow current (lo dV/dt)) -55 mv closed closed OPENS open
Repolarization: Inactivation 2 (loss of slow current) 0 to -50 mv closed closed open CLOSES
Recovery (of excitability) -55 mv closed closed CLOSES OPENS

Note: Gates: a = activation; i = inactivation
TMP = transmembrane potential
"a" = activation; "i" = inactivation
"m" and "h" are upper and lower gates in the Na+ channel.
"d" and "f" are upper and lower gates in the Ca++ channel.

Return to Page 6

Return to Index