F. Kurosaki, ROLE OF INWARD K-MEMBRANE IN SIGNAL CROSS-TALKING OF CAMP WITH CA2+ CASCADE( CHANNEL LOCATED AT CARROT PLASMA), FEBS letters, 408(1), 1997, pp. 115-119
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.