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

Figure 1

Spontaneous electrical activity of rabbit and human sinoatrial node (SAN) pacemaker cells. (a) and (b) Typical examples (a) and average characteristics (b) of action potentials. (c) and (d) Typical examples (c) and average characteristics (d) of the intracellular free Ca²⁺ concentration ([Ca²⁺]_𝑖). Data are mean±SEM; 𝑛=number of cells; MDP=maximum diastolic potential; APA=action potential amplitude; DDR₁₀₀=diastolic depolarization rate over the 100 ms time interval starting at MDP+1 mV; d𝑉_𝑚/d𝑡_max=maximal upstroke velocity; APD₂₀,APD₅₀, and APD₉₀=action potential duration at 20, 50, and 90% repolarization; MDC=minimum diastolic [Ca²⁺]_𝑖; TA=[Ca²⁺]_𝑖 transient amplitude; d[Ca²⁺]_𝑖/d𝑡_max=maximum rate of rise of [Ca²⁺]_𝑖 transient; TD₂₀,TD₅₀, and TD90=[Ca²⁺]_𝑖 transient duration at 20, 50, and 90% decay. ^∗𝑃<0.05.