Figure 1.

Depolarization-evoked increases in [Ca²⁺]_c and contraction

A depolarizing pulse to 0 mV (holding potential -70 mV, C) induced an inward I_Ca (B) and increased [Ca²⁺]_c (A). The inset in A shows the [Ca²⁺]_c, I_Ca and membrane voltage on an expanded time axis. Following the rise in [Ca²⁺]_c contraction occurred (D); this reached a maximum at about the same time as the [Ca²⁺]_c was returning to resting levels; thereafter the cell slowly relaxed with a half time of 17 s. However, [Ca²⁺]_c remained slightly above resting levels for an extended time following depolarization. Time alignment of the video-taped contractile behaviour of the cell (E), with [Ca²⁺]_c, was achieved by illumination of the cell with an LED triggered by depolarization. The depolarization and [Ca²⁺]_c were also digitized and recorded on computer.