Fig. 6. Effect of ISO on the relationship between SR Ca²⁺ uptake and the [Ca²⁺]_i. (A) Representative intracellular Ca²⁺ recordings in control and with 1 µmol l^–1 isoproterenol (ISO). Bars above traces indicate membrane potential (top bar) and extracellular solution (lower bar); –, regular bath solution; +, bath solution with 10 mmol l^–1 caffeine. (B) Effect of membrane potential on the average Ca²⁺ transient during depolarization (black bars) and the peak Ca²⁺ transient elicited by 10 mmol l^–1 Caf (white bars, N=7). (C) Effect of ISO on the relationship between SR Ca²⁺ uptake rate and [Ca²⁺]_i (N=7). Solid (control) and dotted (ISO) lines represent fits of data with a Hill equation.