Cardiomyocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 266

Table 5.14. Main features of CMC potassium carriers.

Inward rectifier Small efflux at positive potential

Open at negative potential
Repolarization down to − 80 mV

Delayed rectifier Phase 3 repolarization

Slow activation beyond

− 40 mV

Slow inactivation

Transient outward Activation by depolarization

Phase 1 repolarization

Muscarinic (ACh) Inward motion

Hyperpolarization
Background current in SAN

ATP Opening by low [ATP],

by increase in [ADP],
and by adenosine, H +

decreases free G level due to the restoration of the activity of regulators of

G-protein signaling. Consequently, the number of active GIRK channels decays
during cardiomyocyte contraction.

βγ

Cardiac ATP-Sensitive K + Channel

Cardiac sarcolemmal ATP-sensitive K + channel (that causes i K AT P current) is
composed of K IR 6.2 and SUR2a subunits, as well as glyceraldehyde 3-phosphate
dehydrogenase. 101 It is regulated by intracellular ATP [ 480 ]. It couples glycolysis
to membrane excitability. ATP-sensitive K + channel is responsible for ST-segment
elevation on ECG during ischemia [ 481 ].

5.10.5 Calcium-Activated Chloride Channels

Calcium-activated Cl − current 102 occurs in the same action potential period as
transient outward K + current and contributes to ventricular repolarization. Main
features of ion carriers are summarized in Tables 5.14 to 5.16 .

101 Enzyme GAPDH produces (1,3)-bisphosphoglycerate, an opener of ATP-sensitive K + channels.
Hence, it regulates the channel activity.
102 Calcium-activated, temperature-dependent Cl − currents can be observed in atrial and ventricular
myocytes, as well as cardiac Purkinje cells, at least in the rabbit heart.