Yb. Ouyang et al., INFLUENCE OF ACID-BASE CHANGES ON THE INTRACELLULAR CALCIUM-CONCENTRATION OF NEURONS IN PRIMARY CULTURE, Experimental Brain Research, 101(2), 1994, pp. 265-271
The influence of changes in intra- and extracellular pH (pH(i) and pH(
e), respectively) on the cytosolic, free calcium concentration ([Ca2+]
(i)) of neocortical neurons was studied by microspectrofluorometric te
chniques and the fluorophore fura-2. When, at constant pH(e), pH(i) wa
s lowered with the NH4Cl prepulse technique, or by a transient increas
e in CO2 tension, [Ca2+](i) invariably increased, the magnitude of the
rise being proportional to Delta pH(i). Since similar results were ob
tained in Ca2+-free solutions, the results suggest that the rise in [C
a2+](i) was due to calcium release from intracellular stores. The init
ial alkaline transient during NH4Cl exposure was associated with a ris
e in [Ca2+](i). However, this rise seemed to reflect influx of Ca2+ fr
om the external solution. Thus, in Ca2+-free solution NH4Cl exposure l
ed to a decrease in [Ca2+](i). This result and others suggest that, at
constant pH(e), intracellular alkalosis reduces [Ca2+](i), probably b
y enhancing sequestration of calcium. When cells were exposed to a CO2
transient at reduced pH(e), Ca2+ rose initially but then fell, often
below basal values. Similar results were obtained when extracellular H
CO3- concentration was reduced at constant CO, tension. Unexpectedly,
such results were obtained only in Ca2+-containing solutions. In Ca2+-
free solutions, acidosis always raised [Ca2+](i). It is suggested that
a lowering of pH(e) stimulates extrusion of Ca2+ by ATP-driven Ca2+/2
H(+) antiport.