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pe coupling
Department of Molecular Physiology and Biological Physics, University
of Virginia, Charlottesville 22906-0011, USA.
We sought to understand the excitation-contraction coupling process
in arterioles. KCl or phenylephrine (PE) was applied via the superfusion
solution or by brief pulsatile ejections from a micropipette onto
unpressurized arterioles (in vitro) from either the guinea pig
small intestine or hamster cheek pouch. With either mode of application,
KCl caused depolarizations that were tightly and predictably correlated
with subsequent constrictions (electromechanical coupling). In
contrast, the relationship between membrane potential and vasoconstriction
in response to phenylephrine was dependent on both stimulus duration
and agonist concentration. Application of short pulses of PE (<
1 s) produced mechanical responses that were dominated by pharmacomechanical
coupling (i.e., they were not associated with changes in membrane
potential). With longer PE stimuli, electromechanical coupling
became more important and dominated microvessel responses. We
conclude that adequate understanding of the signaling process
in microvessels requires a consideration of both concentration
and duration of application. Both the mode and duration of agonist
application affect the relative degree of electromechanical or
pharmacomechanical coupling in response to a vasomotor stimulus.
These observations have important implications for intracellular
and intercellular signaling.
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