Ba²⁺ current oscillations modulated by cyclic AMP and phorbol esters in ras-transformed fibroblasts

An oscillatory influx of divalent cations was measured as Ba²⁺ inward currents (Ba²⁺ current oscillations) by voltage-clamp recording in v-Ki-ras-transformed NIH 3T3 (DT) fibroblasts after activation with bradykinin or serum. Application of forskolin or dibutyryl cyclic AMP onto DT cells initiated Ba²⁺ current oscillations. Increasing intracellular cyclic AMP reduced the amplitude but increased the frequency of the Ba²⁺ current oscillations. Activation of protein kinase C by phorbol esters terminated Ba²⁺ current oscillations. No inhibition of Ba²⁺ current oscillations by phorbol esters was observed in down-regulated cells that had been pretreated with phorbol esters for 24 hrs. The results suggest that Ba²⁺ current oscillations are regulated by intracellular second messengers.