F. Kurosaki et al., INVOLVEMENT OF PLASMA MEMBRANE-LOCATED CALMODULIN IN THE RESPONSE DECAY OF CYCLIC NUCLEOTIDE-GATED CATION CHANNEL OF CULTURED CARROT CELLS, FEBS letters, 340(3), 1994, pp. 193-196
Increase in cytoplasmic cyclic AMP concentration stimulates Ca2+ influ
x through the cyclic AMP-gated cation channel in the plasma membrane o
f cultured carrot cells. However, the Ca2+ current terminated after a
few minutes even in the presence of high concentrations of cyclic AMP
indicating that hydrolysis of the nucleotide is not responsible for st
op of the Ca2+ influx. Cyclic AMP evoked discharge of Ca2+ from inside
-out sealed vesicles of carrot plasma membrane, and it was strongly in
hibited when the suspension of the vesicles was supplemented with 1 mu
M of free Ca2+, while Ca2+ lower than 0.1 mu M did not affect the Ca2
+-release. The Ca2+ flux across plasma membrane was restored from this
Ca2+-induced inhibition by the addition of calmodulin inhibitors or a
nti-calmodulin. These results suggest that Ca2+ influx initiated by th
e increase in intracellular cAMP in cultured carrot cells is terminate
d when the cytosolic Ca2+ concentration reaches the excitatory level i
n the cells, and calmodulin located in the plasma membrane plays an im
portant role in the response decay of the cyclic nucleotide-gated Ca2 channel.