Intracellular pH regulation in neurons from chemosensitive and nonchemosensitive regions of Helix aspersa

Abstract

We used 2′,7′-bis(carboxyethyl)-5(6)-carboxyflourescein (BCECF), a pH-sensitive fluorescent dye, to study intracellular pH (pHi) regulation in neurons in CO2chemoreceptor and nonchemoreceptor regions in the pulmonate, terrestrial snail, Helix aspersa. We studied pHiduring hypercapnic acidosis, after ammonia prepulse, and during isohydric hypercapnia. In all treatment conditions, pHifell to similar levels in chemoreceptor and nonchemoreceptor regions. However, pHi recovery was consistently slower in chemoreceptor regions compared with nonchemoreceptor regions, and pHi recovery was slower in all regions when extracellular pH (pHe) was also reduced. We also studied the effect of amiloride and DIDS on pHi regulation during isohydric hypercapnia. An amiloride-sensitive mechanism was the dominant pHi regulatory process during acidosis. We conclude that pHe modulates and slows pHiregulation in chemoreceptor regions to a greater extent than in nonchemoreceptor regions by inhibiting an amiloride-sensitive Na+/H+ exchanger. Although the phylogenetic distance between vertebrates and invertebrates is large, similar results have been reported in CO2-sensitive regions within the rat brain stem.