Role of inward K+ channel located at carrot plasma membrane in signal cross-talking of cAMP with Ca2+ cascade

Treatment of cultured carrot cells with dibutyryl cAMP or forskolin resulted in the appreciable decrease in extracellular K+ concentration. This decrease was found to be transient and the concentration of the ion in the culture medium restored to the original level within few minutes. The cAMP-induced decrease in K+ level in the medium was almost completely inhibited,when carrot cells mere incubated in the presence of K+ channel blockers, CsCl and tetraethylammonium chloride. Appreciable amounts of Ca-45(2+) mere discharged from Ca-45(2+)-loaded inside-out vesicles of carrot plasma membrane by the stimulation with cAMP, however, the release of the ion was significantly inhibited in the presence of the K+ channel blockers. The release of Ca-45(2+) from the vesicles was also observed when K+ current was evoked with an ionophore, valinomycin, even in the absence of cAMP. These results suggest that the gating of some of the inward K+ channels located at plasma membrane of cultured carrot cells is controlled by cytoplasmic concentration of cAMP and the inward K+ current across the plasma membrane induced by the nucleotide elicits Ca2+ influx into the cells possibly by the activation of voltage-dependent Ca2+ channels. (C) 1997 Federation of European Biochemical Societies.