| Abstract: | Experiments have been carried out with guinea-pig smooth muscles taenia coli by the use of the double sucrose-gap technique. Phorbol esters (PE), activating protein kinase C (PcC) suppressed the spontaneous and induced (by turning on of depolarizing pulses, or turning off a long lasting hyperpolarizing step) electrical and contractile activity of a muscle. The inactive analog of PE did not affect the muscle activity. Na/H-ionophore monensin imitated the effects of active PE. Blockade of K+ channels by 10 mM TEA greatly decreased or in some cases even removed the inhibitory effects of PE. A treatment of the muscle by Na+/H+ exchange inhibitor ethyl isopropyl amiloride (EIPA) increased the amplitude of action potentials during membrane depolarization and markedly weakened the PE-induced suppression of muscle electrical activity. The data obtained suggested that inhibitory effects of PE on smooth muscle electrical and contractile activity resulted from an increase in potassium permeability of the membrane. Na+/H+ exchange seems to be involved in PE-induced K+ channels activation. |
