Figure 3.

Mechanism of the effects of intracellular Na+ concentration ([Na+]i) on diastolic intracellular Ca2+ concentration ([Ca2+]i). A, Original data. Ca transients recorded using indo-1 in a rat ventricular myocyte. Records show the following: left, control; right, in the presence of the Na-K pump inhibitor, strophanthidin. Data reproduced from Bennett et al.²⁰ B, Flowchart. Initially (blue rectangle), Ca²⁺ efflux equals influx. The increase in [Na⁺]_i decreases sodium-calcium exchange (NCX) activity making Ca²⁺ efflux less than influx, leading to an increase in diastolic [Ca²⁺]_i. There will also be an increase in sarcoplasmic reticulum (SR) Ca²⁺ content and thence an increase in systolic [Ca²⁺]_i. The increases of diastolic and systolic [Ca²⁺]_i will increase Ca²⁺ efflux until efflux again equals influx.