The effects of indomethacin on calcium, sodium, potassium and magnesium fluxes in various tissues of the guinea-pig.

1. Isolated tissues of the guinea-pig were bathed with Krebs solution at 37 degrees C and subjected to 100 ms pulses of electrical stimulation for 30 min at a frequency of 0.1 or 1.0 Hz. The tissues were then dried, ashed, and the ash analysed for calcium, sodium, potassium and magnesium.2. Gastric smooth muscle, cardiac and skeletal muscles and brain all showed a gain of sodium and calcium and a loss of potassium in response to electrical stimulation, but there was no significant change in the magnesium content of any of these tissues.3. Indomethacin (0.5 mM) reduced the calcium content of unstimulated gastric smooth muscle and reduced the gain of calcium and sodium in response to electrical stimulation, but slightly increased the net loss of potassium in response to electrical stimulation.4. Gastric smooth muscle which had gained calcium as a result of electrical stimulation, gradually lost it again when stimulation ceased. Indomethacin (0.5 mM) hastened the net loss of calcium from previously stimulated muscle.5. Indomethacin (0.5 mM) failed to alter the calcium, sodium, potassium and magnesium contents of unstimulated cardiac muscle, skeletal muscle and brain. In these tissues indomethacin (0.5 mM) also failed to prevent the changes in the content of these minerals which occurred in response to electrical stimulation.