Journal of Neuroscience, Vol 11, 2130-2134, Copyright © 1991 by Society for Neuroscience
Selectivity of the effects of guanosine-5'-O-(2-thiodiphosphate) on agonist inhibition of the M-current in amphibian sympathetic neurons
MA Simmons and RJ Mather
Department of Pharmacology, Marshall University, Huntington, West Virginia 25755-9310.
In bullfrog sympathetic neurons, luteinizing hormone-releasing hormone,
muscarine, and substance P act as agonists at specific membrane receptors
to decrease a potassium current, IM. The receptors are coupled to guanine
nucleotide-binding proteins (G-proteins). Whole-cell recordings of IM were
made from isolated bullfrog sympathetic neurons to examine the effects of
intracellularly applied guanosine-5'-O-(2- thiodiphosphate) (GDP beta S) on
agonist inhibition of IM. Successive responses to a given agonist were
decreased in the presence of GDP beta s. Subsequent responses to the other
agonists were then measured to determine the degree of overlap of the
effect of GDP beta S for the different agonists. GDP beta S selectively
inhibited successive responses to one agonist such that a subsequent
application of a different agonist was still effective. If GDP beta S acts
at the level of the G-protein, this suggests that each receptor is coupled
to a separate population of G-proteins. Alternatively, GDP beta S may act
at the receptor level to block receptor coupling to IM.