Indapamide-induced inhibition of calcium movement in smooth muscles.

The effects of indapamide on ionic currents and isometric contractions in both rat myometrium and rat portal vein preparations were studied. Indapamide (3 x 10(-4) M) depressed both inward calcium and outward potassium currents. The decrease in potassium current was dependent on the reduction of the inward calcium current. Indapamide reduced the transient contraction induced in calcium-free, ethylene glycol-bis(B-aminoethylether)-N,N'tetra-acetic acid-containing solutions by either acetylcholine (10(-4) M) or norepinephrine (10(-5) M). The results indicate that indapamide acts primarily on the plasma membrane of spontaneously active smooth muscles by reducing the calcium current; it may also depress contractions supported by release of calcium from the sarcoplasmic reticulum.