Nimodipine blocks I_Ca and accompanying [Ca²⁺] increase, but does not decrease resting [Ca²⁺] in voltage-clamped single colonic myocytes. Depolarization (−70 to +10 mV; F) activated a voltage-dependent Ca²⁺ current (I_Ca; E) to increase [Ca²⁺] in the subplasma membrane space (B) and bulk cytoplasm (C). Changes in the fluorescence ratio with time (B and C) are derived from the region encompassing that part of the cell in TIRF (A; right panel). 1 µM nimodipine (D) applied from a puffer pipette (A, left panel) did not alter resting subplasma membrane (B) or bulk average (C) [Ca²⁺] but blocked depolarization-evoked I_Ca (E) and the accompanying [Ca²⁺] rise (B and C). The break in the record is ∼3 min after which I_Ca and accompanying [Ca²⁺] increase partially recovered. A bright field image of the cell is shown in A (left panel); see also whole cell electrode (right side). The inset in C shows the bulk average [Ca²⁺]_c changes, which occurred in a cell using the same protocol except that nimodipine was not puffed onto the cell.