Effects of ursolic acid on contractile activity of gastric smooth muscles.

Ursolic acid (UA) in concentrations of l x 10(7) mol/L - 5 x 10(5) mol/L induced relaxation in gastric smooth muscle (SM) tissues, in a concentration-dependent manner. The relaxation did not change membrane potential and slow wave contraction patterns. A significant decrease in amplitude and frequency of spike- potentials was observed. UA-induced reactivity was removed when SM preparations were treated with nifedipine (1 x 10(6) mol/L). Ca2+-induced contractions of the depolarized SM preparations (42 mmol/L K+; Ca2+-free Krebs solution) were substantially reduced in the presence of UA. It was determined that, in certain concentrations, UA influenced L - type Ca2+ channels, and reduced the Ca2+ influx.