The effect of forskolin on smooth muscle cells of guinea-pig taenia caeci.

Forskolin (0.5-10 microM) caused hyperpolarization and relaxation of the smooth muscle cells of guinea-pig taenia caeci (35 degrees C) as measured with the sucrose-gap method. Membrane conductance, reflected by the amplitude of the electrotonic potential, was not changed during the response. The hyperpolarization could also be evoked in the absence of extracellular calcium, calcium and potassium, or calcium and sodium. Further, the 45Ca2+ efflux from taenia caeci was enhanced by forskolin. The results support the concept that calcium extrusion across the plasma membrane is promoted in the presence of forskolin by stimulation of electrogenic calcium pumping.