Substantial evidence suggests that in disease states such as diabetes and atherosclerosis coronary vasodilation to endothelial derived nitric oxide is reduced. An important and widely recognized mechanism of this impairment involves heightened oxidant stress, largely due to superoxide, which occurs In these disease states. Dilator mechanisms operating through vascular smooth muscle hyperpolarization, Including endothelial- derived hyperpolarization factor (EDHF), are exposed to the same oxidative stress in diabetes and atherosclerosis, but little is known about the effect of reactive oxygen species on mediators of vascular smooth muscle hyperpolarization. This may be very important in humans where we have previously shown that in vascular smooth muscle, hyperpolarization by EDHF or by openers of ATP-sensitive potassium channels plays a more prominent role in physiological and pharmacological vasodilation of coronary resistance vessels. Our overall objective is to determine how superoxide influences human coronary arteriolar dilation that is mediated by smooth muscle hyperpolarization.
In aim 1 we shall examine the hypothesis that superoxide impairs vasodilation to activation of KATP (but not BKCa [calcium-activated] K+- channels).
In aim 2 we shall determine the effect of a pathophysiologically relevant state of increased oxidative stress (atherosclerosis and diabetes) on KATP and BKCa channel-mediated dilation and channel opening. Preliminary data suggest that coronary dilation mediated by KATP but not BKCa channels is impaired in patients with DM and CAD. This will be extended to hypoxic coronary dilation which is mediated by KATP channels in humans. Since hyperglycemia is associated with increased oxidant stress, in aim 3 we shall determine the effect of high glucose on hyperpolarization-mediated dilation of human coronary arterioles. Fresh human coronary arterioles isolated from myocardial tissue (during cardiopulmonary bypass) are mounted onto micropipettes and pressurized for diameter measurements using in vitro videomicroscopy. Isolated human coronary arteriolar smooth muscle cells will be prepared for patch- clamp analysis of potassium channel currents. This combination of pharmacological and electrophysiological assessment of vascular and cellular function provides a powerful mechanism for studying hyperpolarization-dependent vascular regulatory processes in health and disease. These studies will have important implications with regard to coronary vasomotor regulation. Coronary arterioles responsible for regulating myocardial perfusion (between 50-150 microns in diameter) will be studied. The proposed experiments should identify, in human subjects, novel mechanisms of altered coronary vasoregulation. The results could suggest new therapeutic approaches for improving vascular function in patients with diabetes and coronary disease.