Figure 2. Apparent threshold for Ca-P_i precipitation.

Effect of stopping bath perfusion following equilibration with solutions containing various [P_i]. At each [P_i], introduction of P_i resulted in a transient increase in Ca²⁺ due to SR Ca²⁺ release. At 1 and 2 mm P_i, the [Ca²⁺] remained constant when the flow was subsequently stopped. At 5 mm P_i, a small maintained decrease in [Ca²⁺] occurred when the flow was stopped. At higher [P_i], the initial [Ca²⁺] release was followed by a maintained decrease in the steady state [Ca²⁺]. The fall in [Ca²⁺] that occurred when the flow was stopped became progressively greater as the [P_i] was increased above 5 mm. All responses were obtained in the same mechanically skinned preparation. The [Ca²⁺] of the bathing solution was 100 nm and the free [Mg²⁺], 1 mm. The vertical bar indicates a change in ratio of 0.1 units. All responses were obtained in the same preparation.