Db. Jennings, RESPIRATORY CONTROL DURING EXERCISE - HORMONES, OSMOLALITY, STRONG IONS, AND PACO(2), Canadian journal of applied physiology, 19(3), 1994, pp. 334-349
For optimal performance of exercising muscle, the charge state of prot
eins must be maintained; the pH environment of protein histidine imida
zole groups must be coordinated with their pK. During exercise, increa
sing temperature and osmolality as well as changes in strong ions affe
ct the pK of imidazole groups. Production of strong organic anions als
o den eases the concentration difference between strong cations and an
ions (strong ion difference, or [SID]), causing a metabolic acidosis i
n peripheral tissues. Central chemoreceptors regulate Peg in relation
to the [SID] of brain fluids to maintain a ''constant'' brain [H+]. In
addition, increased osmolality, angiotensin II, and vasopressin durin
g exercise may stimulate circumventricular organs of the brain and int
eract with chemical control of ventilation. Changes in [SID] of brain
fluids during exercise are negligible compared to systemic decreases i
n [SID]; thus, regulation of Pco(2) to maintain brain [H+] homeostasis
cannot simultaneously compensate for greater changes in [SID] in peri
pheral tissues.