ROLE OF INWARD K-MEMBRANE IN SIGNAL CROSS-TALKING OF CAMP WITH CA2+ CASCADE( CHANNEL LOCATED AT CARROT PLASMA)

Treatment of cultured carrot cells with dibutyryl cAMP or forskolin re sulted in the appreciable decrease in extracellular K+ concentration. This decrease was found to be transient and the concentration of the i on in the culture medium restored to the original level within few min utes. The cAMP-induced decrease in K+ level in the medium was almost c ompletely inhibited,when carrot cells mere incubated in the presence o f K+ channel blockers, CsCl and tetraethylammonium chloride. Appreciab le amounts of Ca-45(2+) mere discharged from Ca-45(2+)-loaded inside-o ut vesicles of carrot plasma membrane by the stimulation with cAMP, ho wever, the release of the ion was significantly inhibited in the prese nce of the K+ channel blockers. The release of Ca-45(2+) from the vesi cles was also observed when K+ current was evoked with an ionophore, v alinomycin, even in the absence of cAMP. These results suggest that th e 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 acti vation of voltage-dependent Ca2+ channels. (C) 1997 Federation of Euro pean Biochemical Societies.