Intracellular pH regulation and the acid delusion.

The hydrogen ion concentration ([H+]) in intracellular cytoplasmic fluid (ICF) must be maintained in a narrow range in all species for normal protein functions. Thus, mechanisms regulating ICF are of fundamental biological importance. Studies on the regulation of ICF [H+] have been hampered by use of pH notation, failure to consider the roles played by differences in the concentration of strong ions (strong ion difference, SID), the conservation of mass, the principle of electrical neutrality, and that [H+] and bicarbonate ions [HCO3-] are dependent variables. This argument is based on the late Peter Stewart's physical-chemical analysis of [H+] regulation reported in this journal nearly forty years ago (Stewart. 1983. Can. J. Physiol. Pharmacol. 61: 1444-1461. Doi:10.1139/y83-207). We start by outlining the principles of Stewart's analysis and then provide a general understanding of its significance for regulation of ICF [H+]. The system may initially appear complex, but it becomes evident that changes in SID dominate regulation of [H+]. The primary strong ions are Na+, K+, and Cl-, and a few organic strong anions. The second independent variable, partial pressure of carbon dioxide (PCO2), can easily be assessed. The third independent variable, the activity of intracellular weak acids ([Atot]), is much more complex but largely plays a modifying role. Attention to these principles will potentially provide new insights into ICF pH regulation.

Renal collecting duct physiology and pathophysiology 1.

In the kidney, the collecting duct (CD) is composed of at least four cell types: principal, type-A intercalated cells (IC), type-B IC, and non-A and non-B IC. Although this heterogeneous composition has been recognized since the end of the nineteenth century, the physiological role of the various cell types in the CD continues to be deciphered as of today. Principal and ICs are essential in ion-water balance and acid-base homeostasis, respectively. However, recent research has revealed a striking interplay and overlap between the specific functions of these cell types. This review summarizes the recent findings on CD cells and their role in multiple pathophysiologies.

[Acid-base homeostasis: metabolic acidosis and metabolic alkalosis]. / Équilibre acidobasique: acidoses et alcaloses métaboliques.

Acid-base homeostasis ensured by the kidneys, which maintain the equilibrium between proton generation by cellular metabolism and proton excretion in urine. This requirement is lifesaving because of the protons' ability to bind to anionic proteins in the extracellular space, modifying their structure and functions. The kidneys also regenerate bicarbonates. The kidney is not the sole organ in charge of maintaining blood pH in a very narrow range; lungs are also involved since they allow a large amount of volatile acid generated by cellular respiration to be eliminated.