Smooth muscle contraction is mediated by an increase in the concentration of cytoplasmic free calcium. 2. Low concentrations of caffeine can induce transient contraction of smooth muscle through the release of intracellular calcium from intracellular storage sites. 3. The current study determined the effect of caffeine (0.4-100 microM) on the response of the in vitro whole bladder preparation to field stimulation (FS) at 0.6, 1.8, and 5.4 mM extracellular calcium. 4. The following parameters were determined: basal pressure (BP), peak pressure response (PP), maximal rate of pressure generation (PR), maximal rate of bladder emptying (RE), and percent of volume emptied (VE). 5. The results demonstrated that in the absence of caffeine, BP, PP, and PR were increased progressively as a function of both frequency of stimulation and the concentration of calcium. 6. In addition, caffeine significantly increased the rate of pressure generation at 0.6 and 1.8 mm calcium.
