Carbon monoxide as an endogenous vascular modulator

Area of Science:

• Biochemistry
• Physiology
• Vascular Biology

Background:

• Carbon monoxide (CO) is a product of heme oxygenase (HO)-catalyzed heme degradation.
• Two isoforms, HO-1 (inducible) and HO-2 (constitutive), exist, with HO-2 predominantly expressed in vascular cells and brain astrocytes.
• HO-2 activity is modulated by heme levels, protein phosphorylation, and calcium signaling.

Purpose of the Study:

• To explore the physiological roles of the heme oxygenase/carbon monoxide (HO/CO) system in circulatory regulation.
• To elucidate the mechanisms by which CO influences vascular tone, particularly in cerebral circulation.
• To understand the protective functions of the HO/CO system in the vasculature.

Main Methods:

• Investigated CO production via heme oxygenase (HO) activity.
• Examined the effects of CO on cerebral, skeletal muscle, and renal arterioles.
• Analyzed the interaction of CO with large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels.
• Assessed the influence of prolonged CO exposure on nitric oxide synthase (NOS) activity.
• Evaluated the protective roles of CO and bilirubin against oxidative stress and apoptosis.

Main Results:

• CO, primarily from HO-2 in vascular cells, causes vasodilation, notably in cerebral arterioles.
• CO-mediated dilation involves activation of smooth muscle cell BK(Ca) channels.
• Inhibition of HO attenuates vasodilation induced by various stimuli like seizures and hypoxia.
• Prolonged elevated CO constricts cerebral arterioles by inhibiting nitric oxide synthase.
• The HO/CO system demonstrates significant vascular protective effects, including anti-apoptotic and antioxidant properties.

Conclusions:

• The HO/CO system plays a critical role in regulating vascular tone and protecting the vasculature.
• HO-2 derived CO is a key mediator of cerebral vasodilation.
• While acute CO causes dilation, chronic exposure can lead to vasoconstriction via NOS inhibition.
• Further research is needed to fully understand the complex physiology and biochemistry of the HO/CO system in circulation.