Figure 4. Membrane depolarisation and Ca²⁺ store refilling.

A, carbachol-induced Ca²⁺ transients before and after zero-Ca²⁺ solution. Two Ca²⁺ transients are superimposed after the zero-Ca²⁺ solution, in 1.8 mm Tyrode solution containing either 4 mm or 24 mm KCl. B, a similar format to A in which the cell membrane potential (E_m) was held under voltage clamp. Two carbachol-induced Ca²⁺ transients are superimposed after zero-Ca²⁺ solution: one after the cell was briefly depolarised to −25 mV, the other when E_m was held constant at −60 mV throughout. C, carbachol-induced Ca²⁺ transients in a detrusor cell under voltage clamp in Ca²⁺-containing Tyrode solution throughout. The cell was briefly depolarised from −60 to −25 mV between the second and third transients.