Differential effects of cAMP and serotonin on membrane current, action-potential duration, and excitability in somata of pleural sensory neurons of Aplysia
D. A. Baxter and J. H. Byrne Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225. 1. In somata of sensory neurons in the pleural ganglia of Aplysia californica, serotonin (5-HT) modulates at least three K+ currents: the S K+ current (IK,S), a slow component of t...
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Veröffentlicht in: | Journal of neurophysiology 1990-09, Vol.64 (3), p.978-990 |
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Zusammenfassung: | D. A. Baxter and J. H. Byrne
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225.
1. In somata of sensory neurons in the pleural ganglia of Aplysia
californica, serotonin (5-HT) modulates at least three K+ currents: the S
K+ current (IK,S), a slow component of the Ca2(+)-activated K+ current
(IK,Ca), and the delayed or voltage-dependent K+ current (IK,V). The
modulation of IK,S and the slow component of IK,Ca by 5-HT has been shown
previously to be mediated via adenosine 3',5'-cyclic monophosphate (cAMP).
To determine whether the modulation of IK,V by 5-HT also is mediated via
cAMP, we used two-electrode voltage-clamp techniques to compare the
modulation of membrane current by cAMP and 5-HT. 2. Current responses were
elicited by brief (200 ms) voltage-clamp pulses before and after the bath
application of analogues of cAMP. At all voltage-clamp potentials examined
(-40-30 mV), analogues of cAMP reduced the amplitude of the current
response. The properties of the cAMP-sensitive component of membrane
current were revealed by computer subtraction of current responses elicited
in the presence of the analogue of cAMP from current responses elicited
before application of the analogue. The characteristics of the resulting
cAMP difference current (IcAMP) suggested that cAMP modulated a component
of membrane current that was relatively voltage independent, did not
inactivate, and was active over a wide range of membrane potentials. In
addition, the current-voltage (I-V) relationship of the cAMP difference
current had a positive slope. These properties of the cAMP difference
current were consistent with those of IK,S but did not indicate that IK,V
was modulated by cAMP. 3. The cAMP-independent modulation of membrane
current by 5-HT was examined by eliciting current responses first in the
presence of an analogue of cAMP and again after the addition of 5-HT to the
bath, which still contained the analogue. The presence of the analogue of
cAMP occluded further modulation of IK,S by 5-HT. However, the analogue of
cAMP did not occlude the modulation of IK,V by 5-HT. This cAMP-independent
effect of 5-HT on membrane current was revealed by computer subtraction of
current responses elicited in the presence of 5-HT from current responses
elicited before the application of 5-HT (the analogue of cAMP was present
throughout). The resulting cAMP-independent 5-HT difference current (I5-HT)
was highly voltage dependent, had complex kinetics, and |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.1990.64.3.978 |