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 were incubated in the presence of K+ channel blockers, CsCl and tetraethylammonium chloride. Appreciable amounts of 45Ca2+ were discharged from 45Ca2+-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 45Ca2+ 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.
Kurosaki
F
F
Cell Biology Laboratory, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Sugitani, Japan. kurosaki@ms.toyama-mpu.ac.jp
D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D018552:Daucus carota / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology; D007476:Ionophores / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D015398:Signal Transduction; D014634:Valinomycin / Q000494:pharmacology
D007476:Ionophores; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D005576:Colforsin; D014634:Valinomycin; D003994:Bucladesine; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium