CYCLIC 3',5' AMP RELAY IN DICTYOSTELIUM-DISCOIDEUM .2. REQUIREMENTS FOR THE INITIATION AND TERMINATION OF THE RESPONSE
CYCLIC 3',5' AMP RELAY IN DICTYOSTELIUM-DISCOIDEUM .2. REQUIREMENTS FOR THE INITIATION AND TERMINATION OF THE RESPONSE
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DOI：
10.1083/jcb.80.2.300
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发表时间：
1979-01-01
影响因子：
7.8
通讯作者：
STECK, TL
中科院分区：
文献类型：
--
作者：
DEVREOTES, PN;STECK, TL
The secretion of 3H-cyclic AMP (cAMP) by prelabeled and suitably differentiated D. discoideum amoebae was elicited in a perfusion apparatus by 10-10 to 10-5 M [14C]cAMP stimuli of defined magnitude and duration. Exogenous stimuli evoked an immediate increase deceleration in [3H]cAMP secretion which accelerated continuously to reach a peak of up to 100 times the unstimulated rate after 2-3 min of stimulation. Withdrawal of the stimulus at any time during the response led to a rapid decline to basal levels. A spontaneous decline in secretion rate was observed during prolonged cAMP stimulation, with a return to basal levels after 3-8 min of stimulation. After the initial secretory event, cells did not respond further to the continued presence of external [14C]cAMP unless it was interrupted by a brief recovery period or the level of the stimulus was increased sufficiently. Since the 2nd increment could follow the 1st at any time, continuous secretion of [3H]cAMP could be sustained for up to 30 min by progressively increasing the stimulus between 10-10 and 10-5 M cAMP. The total magnitude of spontaneously terminated responses depended on the size of the increment in applied cAMP, larger stimuli evoking both a more rapid acceleration and a slower deceleration in [3H]cAMP secretion rate. The integrated response to a given increment in stimulus level was apparently independent of its shape, i.e., the duration, magnitude and number of sub-steps in the increment. These data support 2 mechanistic inferences: that amoebae respond in proportion to relative increases in extracellular cAMP concentration, but adapt to the concentration of cAMP itself. Apparently the initiation and termination of the response are mediated by cellular component(s) beyond cAMP-occupied receptors.
