Calcium Transient and Sodium-Calcium Exchange Current in Human versus Rabbit Sinoatrial Node Pacemaker Cells

Figure 2

(a), Simultaneously recorded action potential (top) and [Ca²⁺]_𝑖 transient (bottom) of a rabbit SAN cell. (b) Time derivatives of the action potential (top) and [Ca²⁺]_𝑖 transient (bottom) traces shown in panel (a). Arrows indicate the timing of the maximum rate of change in membrane potential (d𝑉_𝑚/d𝑡_max) and intracellular Ca²⁺ concentration (d[Ca²⁺]_𝑖/d𝑡_max). Horizontal bar indicates the time lag of ≈20 ms. (c) Time lag between the occurrence of d𝑉_𝑚/d𝑡_max and d[Ca²⁺]_𝑖/d𝑡_max versus beating frequency of the 7 cells measured. Solid line is the linear regression line (slope 0.1±1.1;𝑅=0.042). Note the absence of an appreciable frequency dependence of the time lag.

(a)

(b)

(c)