Effects of low pH on the mechanical response of thin-fiber muscle afferents that may be associated with exercise pressor reflex

Abstract

Cardiovascular and respiratory responses are reflexly augmented during exercise, and the former is known as the exercise pressor reflex. The exercise pressor reflex is thought to be caused by both mechanical and metabolic stimuli to thin-fiber muscle afferents innervating active skeletal muscles. Ischemia induced-acidosis has been reported to augment the exercise pressor reflex. However, protons alone do not excite many thin-fiber afferents. In this short review, we show that protons lower the response threshold and increase the response magnitude to mechanical stimulation of thin-fiber muscle afferents, thus possibly contributing to the exercise pressor reflex. Furthermore, this short review introduces a new sensitizing mechanism by protons (low pH) of thin-fiber muscle afferents via a type of extracellular matrix proteoglycan, versican. The possibility of controlling the augmented reflex during ischemic exercise in people with cardiovascular disease is also discussed.