Vasomotor responses, triggered at discrete locations on arterioles by micropipet release of acetylcholine (ACh; dilation), norepinephrine (NE; constriction), or KCI (constriction), are conducted over distances which encompass several millimeters and multiple branches. Conduction appears integral to the local control of tissue blood flow; conducted (but not localized) vasodilation increases microvascular perfusion and attenuates sympathetic vasoconstriction. Nevertheless, the signal(s) which underlie conduction are unknown. Our working hypothesis is that conduction of vasomotor responses reflects the triggering of a change in membrane potential (Em) which spreads cell-to-cell along the arteriolar wall, resulting i diameter responses via 'electromechanical' coupling. Foremost, the correspondence between vasomotor activity and electrical events in the cells which comprise arterioles is undefined. Therefore, using he hamster cheek pouch preparation to facilitate intracellular microelectrode access to arterioles in vivo, our First Aim is to determine the relationship between Em and arteriole diameter at defined stimulus concentrations during cumulative dose-response curves to ACh, NE, and KCI; nitroprusside (NP), a dilator which does not induce conduction, will also be evaluated. These experiments will provide fundamentally new insight into the sole of electromechanical vs. pharmacomechanical coupling in the control of arteriole resistance.
Our Second Aim i s to investigate the intracellular events which correspond to the conduction of vasodilation and vasoconstriction in arteriole networks. ACh, NP, NE, and KCI will be applied with micropipets to specific site in defined arteriole networks while measuring Em and arteriole diameter simultaneously at established conduction distances (500 to 1500 mum) from the stimulus site. These experiments will define the role of electrical signaling between cells in the conduction of vasomotor responses. Whereas homologous gap-junctional coupling is clearly demonstrated between endothelial cells and between smooth muscle cells,, heterologous coupling between endothelial and smooth muscle cells remains controversial. Using microinjection of Lucifer Yellow dye to label cells during recording, our Third Aim is to determine endothelial cell-and smooth muscle cell-specific responses which correspond to the initiation and conduction of vasodilation and vasoconstriction. Our long-term goal is to understand the role of cell-to-cell communication in coordinating the local control of tissue blood flow. Current knowledge of vascular cell physiology is based largely upon cultured and isolated vascular preparations. While such models have provided valuable information, it is essential that cellular mechanisms of flow control be investigated in the living microcirculation. Findings from these experiments will provide unique insight into the dynamic control of network resistance and will be used to develop a novel foundation from which to test hypotheses regarding microvascular pathophysiology in diseased conditions.
Showing the most recent 10 out of 36 publications
