PATTERNS OF EXCITATION-CONTRACTION COUPLING IN ARTERIOLES - DEPENDENCE ON TIME AND CONCENTRATION

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 unp ressurized arterioles (in vitro) from either the guinea pig small inte stine or hamster cheek pouch. With either mode of application, KCl cau sed depolarizations that were tightly and predictably cor related with subsequent constrictions (electromechanical coupling). In contrast, t he relationship between membrane potential and vasoconstriction in res ponse to phenylephrine was dependent on both stimulus duration and ago nist concentration. Application of short pulses of PE (<1 s) produced mechanical responses that were dominated by pharmacomechanical couplin g (i.e., they were not associated with changes in membrane potential). With longer PE stimuli, electromechanical coupling became more import ant and dominated microvessel responses. We conclude that adequate und erstanding of the signaling process in microvessels requires a conside ration of both concentration and duration of application. Both the mod e and duration of agonist application affect the relative degree of el ectromechanical or pharmacomechanical coupling in response to a vasomo tor stimulus. These observations have important implications for intra cellular and intercellular signaling.