The long-term goal of this laboratory is to forward our understanding of vascular neuroeffector mechanisms specifically related to plurichemical neurotransmission. The evidence is substantial that the resistive and capacitative vessels in the splanchnic circulation differ in their mechanical, electrical, and neurochemical responses to sympathetic nerve stimulation. However, the mechanisms by which neuroeffector processes differ in the arteries and veins remain unknown.
In Aim 1 we propose to examine the hypothesis that the amount and/or ratio of neurally released norepinephrine (NE) and adenosine 5'-triphosphate (ATP) differ in artery and vein due to different expression levels or functional activity of neuronal Ca2+ channel proteins.
Aim 2 is based on our recent observation that activation of postganglionic nerve terminals in mesenteric arteries and veins evokes release of adenosine 5'-diphosphoribose (ADPR), along with ATP, ADP, AMP, adenosine and NE. This represents a novel finding that may lead to identifying new mechanisms of neurovascular control. Arteries and veins show quantitative and qualitative differences in ADPR release. With regard to this, we propose to examine the hypothesis that the formation (primarily CD38-mediated) and release of ADPR or its precursors, NAD+ and cyclic ADPR, are differentially modulated by the activation of protein kinase A (PKA)-dependent pathways in artery and vein.
In Aim 3 we hypothesize that electrical responses to nerve stimulation and NE are mediated by adrenoceptor/PI3-kinase/PKC regulation of Ca2+-activated CI- channels, which may have differential prevalence in artery and vein. These studies will involve experiments in canine mesenteric artery and vein to determine the nerve-evoked overflow of nucleotides, nucleosides and NE (HPLC-FLD and ECD techniques); neuronal Ca2+ channel expression and function (Western blotting, neurotransmitter release); PKA/CD38 interactions (immunoblotting, coprecipitation, protein phosphorylation, RT-PCR), as well as mechanisms of NE activation of ICaCI (patch-clamp techniques). This unprecedented combination of approaches should provide important insight into the complex mechanisms governing neural control in arteries and veins. The results may suggest strategies for interrupting or preventing pathological conditions associated with sympathetic hyperactivity and vascular dysfunctions such as hypertension, cardiogenic shock, congestive heart failure, hemorrhage.
