Table 1 Main ionic currents and their proteins, gens, and function in cardiac SA node of human and small animals mediating excitable activity

If

HCN1, HCN4

hHCN1, hHCN4

Na⁺

Inward

Involves in Diastolic depolarization

Yes,

HCN1, HCN4

Yes,

HCN1 > HCN4

Yes,

HCN4 > HCN1

Yes,

HCN4

 > HCN2

 > HCN1 in mouse

[31, 32, 35, 36, 39,40,41]

Ist

CaV1.3

CACNA1D

Na⁺

Inward

Involves in Diastolic depolarization

Yes?

Yes,

CaV1.3

Yes,

CaV1.3

Yes,

CaV1.3

[31, 33, 34]

ICaT

Cav3.1, Cav3.3

CACNA1G,

CACNA1I

Ca²⁺

inward

contributes to the final phase of diastolic depolarization

Yes,

Cav3.1, Cav3.3

Yes,

Cav3.1, Cav3.3

Yes,

Cav3.1, Cav3.3

Yes,

Cav3.1 > Cav3.2

[31, 33, 35, 36, 39]

ICaL

Cav1.3, Cav1.2

CACNA1D

CACNA1C

Ca²⁺

Inward

Responsible for the SA node action potential upstroke

Yes,

Cav1.3 > Cav1.2

Yes,

Cav1.3 > Cav1.2

Yes,

Cav1.3,Cav1.2

Yes,

Cav1.2 > Cav1.3

[31, 33, 35, 36, 39, 41]

INCX

NCX1, NCX2

SLC8A1

Na⁺ , Ca²⁺

Inward/outward

contribute to the final phase of diastolic depolarization

Yes,

NCX1, NCX2

Yes,

NCX1, NCX2

Yes,

NCX1, NCX2

Yes,

NCX1, NCX2

[31, 35,36,37,38,39, 41]

IKr

Kv11.1

KCNH2

K⁺

Outward

Responsible for repolarization of the SAN AP

Yes,

Kv11.1

Yes,

?

– ?

Yes,

Kv11.1

[31, 35, 36, 39, 41]

IKs

Kv7.1

KCNQ1

K⁺

Outward

Responsible for repolarization of the SAN AP

Yes,

Kv7.1

Yes,

Kv7.1

Yes,

Kv7.1

Yes

Kv7.1

[31, 35, 36, 39]

IK1

Kir2.1/Kir2.2

KCNJ2

K⁺

Outward/inward

Responsible for end of repolarization of the SAN AP and Resting potential

Yes,

Kir2.1/Kir2.2

Yes,

Kir2.1

?

Yes,

Kir3.4

[31, 35, 36, 39,40,41]

Connexins (Cx)

Cx45, Cx40, Cx43

GJC1, GJA5, GJA1

Non-specific ion channels

Bidirectional

Couples the neighboring cells as relatively weakly

Yes,

Cx45, Cx40

Yes,

Cx43, Cx45, Cx40

Yes,

Cx43, Cx45, Cx40

Yes

Cx45

[31, 35, 39, 41, 42]