Oxygen sensing in the carotid body and its relation to heart failure

Angiotensin and carotid body chemoreception in heart failure

The carotid body (CB) plays an important role in the control of breathing and in autonomic control of cardiovascular function. CB chemoreceptor activity is enhanced in chronic heat failure (CHF) and contributes to the sympathetic hyperactivity that exacerbates the progression of the disease. Studies in the past few years have revealed that a local angiotensin (Ang) system exists in the CB and plays an important role in altering CB function in CHF as well as other conditions, such as chronic hypoxia. This brief review highlights recent revelations that Ang I metabolites exert effects within the CB, and focuses on the influence of Ang II and Ang-(1-7) on CB function in CHF.

A crucial role for hydrogen sulfide in oxygen sensing via modulating large conductance calcium-activated potassium channels

Hydrogen sulfide (H(2)S) is an important signaling molecule produced from L-cysteine by cystathionine beta-synthetase (CBS) or cystathionine gamma-lyase (CSE). Here we examined the role of H(2)S in the oxygen-sensing function of the carotid body chemoreceptors, where the large conductance Ca(2+)-activated potassium channel (BK(Ca)) plays a key role. In the isolated mouse carotid body/sinus nerve preparations, the H(2)S donor, NaHS, excited the chemoreceptor afferent nerves in a concentration-dependent manner that was reversed by carbon monoxide donor. The NaHS-evoked excitation was abolished by removing extracellular Ca(2+), or using Cd(2+), pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid and hexomethonium, suggesting that H(2)S evokes release of ATP/ACh from type I glomus cells of the carotid body. The chemoreceptor afferent activation by hypoxia was decreased remarkably using CBS inhibitors, amino oxyacetic acid (AOAA) and hydroxylamine, but not CSE inhibitors, propargylglycine and beta-cyano-L-alanine, despite expression of both enzymes in type I glomus cells. In these cells, the BK(Ca) currents were inhibited by hypoxia and such inhibition was mimicked by NaHS and diminished by AOAA. Finally, mice hyperventilated in response to hypoxia, which was prevented by CBS inhibitors. These data suggest that H(2)S plays a crucial role in mediating the response of carotid body chemoreceptors to hypoxia via modulating the BK(Ca) channels.

Wound healing essentials: let there be oxygen

The state of wound oxygenation is a key determinant of healing outcomes. From a diagnostic standpoint, measurements of wound oxygenation are commonly used to guide treatment planning such as amputation decision. In preventive applications, optimizing wound perfusion and providing supplemental O(2) in the perioperative period reduces the incidence of postoperative infections. Correction of wound pO(2) may, by itself, trigger some healing responses. Importantly, approaches to correct wound pO(2) favorably influence outcomes of other therapies such as responsiveness to growth factors and acceptance of grafts. Chronic ischemic wounds are essentially hypoxic. Primarily based on the tumor literature, hypoxia is generally viewed as being angiogenic. This is true with the condition that hypoxia be acute and mild to modest in magnitude. Extreme near-anoxic hypoxia, as commonly noted in problem wounds, is not compatible with tissue repair. Adequate wound tissue oxygenation is required but may not be sufficient to favorably influence healing outcomes. Success in wound care may be improved by a personalized health care approach. The key lies in our ability to specifically identify the key limitations of a given wound and in developing a multifaceted strategy to specifically address those limitations. In considering approaches to oxygenate the wound tissue it is important to recognize that both too little as well as too much may impede the healing process. Oxygen dosing based on the specific need of a wound therefore seems prudent. Therapeutic approaches targeting the oxygen sensing and redox signaling pathways are promising.