Cell shrinkage stimulates bradykinin-induced cell membrane potential oscillations in NIH 3T3 fibroblasts expressing the ras-oncogene

In NIH 3T3 fibroblasts expressing the Ha-ras oncogene (+ras) bradykinin leads to sustained oscillations of cell membrane potential due to oscillations of intracellular Ca²⁺ with subsequent activation of Ca²⁺-sensitive K⁺ channels. In cells not expressing the oncogene (-ras), bradykinin leads only to a single transient hyperpolarization of the cell membrane. The present study has been performed to elucidate the possible interaction of cell volume, intracellular pH and bradykinin-induced oscillations of the cell membrane potential. Bradykinin leads to cell shrinkage and intracellular alkalinization of both +ras cells and –ras cells. Inhibition of Na⁺/H⁺ exchanger by HOE 694 abolishes the bradykinin-induced alkalinization but does not significantly interfere with the bradykinin-induced oscillations of cell membrane potential. In contrast, prevention of bradykinin-induced cell shrinkage by simultaneous reduction of extracellular osmolarity blunts the oscillations. Thus, cell shrinkage stimulates bradykinin-induced oscillations of cell membrane potential. On the other hand, cell shrinkage alone does not elicit oscillations unless, in addition, Ca²⁺ entry is stimulated by ionomycin.