Effect of extracellular calcium and calcium channel antagonists on ATP and field stimulation induced contractions of the mouse urinary bladder.

1. The dependence on extracellular calcium of the response to the electrical stimulation, ATP and high K induced contractions has been studied in the mouse urinary bladder. 2. The responses to ATP, field stimulation and K induced depolarization were eliminated in calcium free EGTA medium. However, a small remanent of these responses was observed in the absence of calcium in the superfusing medium. 3. The calcium antagonists verapamil, nifedipine and diltiazem decreased in a dose dependent manner the contractions induced by ATP and electrical stimulation of the mouse urinary bladder. 4. The responses of the mouse urinary bladder to high K concentration were antagonized by verapamil and diltiazem, but nifedipine was less effective in decreasing the tonic component of the contraction induced by K in the muscle. 5. The responses of the mouse urinary bladder to electrical stimulation, ATP and high concentration of K are mainly dependent on the extracellular calcium.