Persistent Ca²⁺ sparklets in a voltage-clamped single colonic myocyte. At −70 mV, persistent Ca²⁺ influx occurred in one site (C, region 2) of the cell as measured in TIRF and revealed by the occurrence of persistent Ca²⁺ sparklets. The dihydropryidine blocker of L-type voltage-dependent Ca²⁺ channels, nimodipine (1 µM), applied from a puffer pipette (D) abruptly halted sparklet activity. The latter result suggests that sparklets were derived from the activity of L-type Ca²⁺ channels. Nimodipine produced little change in [Ca²⁺] in other regions (1 and 3–5) of the cell. The [Ca²⁺]_PM images (B) were derived from the time points indicated by the corresponding numerals in C. Changes in the fluorescence ratio with time (C) were derived from 1-pixel boxes (Regions 2–5 in A c and expanded view in A d) and from a larger region encompassing the part of the cell in TIRF (Region 1; A, c and d). The latter was used to obtain an average subplasma membrane [Ca²⁺]_PM change (C). (A, a) A bright field image of the cell; see also whole cell electrode (right side) and 1 µM nimodipine–containing puffer pipette. Persistent Ca²⁺ sparklets were seen in 2 of 306 cells.