Developmental changes in intracellular pH regulation in medullary neurons of the rat

We examined intracellular pH (pH(i)) regulation in the retrotrapezoid nucle us (RTN), a CO2-sensitive site, and the hypoglossal nucleus, a nonchemosens itive site, during development (postnatal days 2-18) in rats. Respiratory a cidosis [10% CO2, extracellular pH (pH(o)) 7.18] caused acidification witho ut pH(i) recovery in the RTN at all ages. In the hypoglossal nucleus, pH(i) recovered in young animals, but as animal age increased, the slope of pH(i ) recovery diminished. In animals older than postnatal day 11, the pH(i) re sponses to hypercapnia were identical in the hypoglossal nucleus and the RT N, but hypoglossal nucleus and RTN neurons could regulate pH(i) during intr acellular acidification at constant pHo at all ages. Recovery of pH(i) from acidification in the RTN depended on extracellular Na+ and was inhibited b y amiloride but was unaffected by DIDS, suggesting a role for Na+/H+ exchan ge. Hence, pH(i) regulation during acidosis is more effective in the hypogl ossal nucleus in younger animals, possibly as a requirement of development, but in older juvenile animals (older than postnatal day 11), pH(i) regulat ion is relatively poor in chemosensitive (RTN) and nonchemosensitive nuclei (hypoglossal nucleus).