Figure 2.

(A) Simulations of the point model. (A) Responses to short Na⁺-pulses. Solid black line: reponse to simultaneous Ca²⁺ and Na⁺ pulses, dashed lines: responses to separate Ca²⁺ and Na⁺ pulses, solid blue line: linear summation of independent responses. The two Na⁺ pulses differ in amplitude. (B) Responses to prolonged Na⁺ elevations of different amplitudes; Na⁺ influx lasts from t = 50 to t = 500 s; at t = 200 s and t = 600 s short Ca²⁺ pulses are given. Black lines: NCX model with allosteric regulation by Na⁺ and Ca²⁺, blue lines: NCX model without allosteric regulation.