Rapid rise of extracellular pH evoked by neural activity is generated by the plasma membrane calcium ATPase.
In hippocampus, synchronous activation of CA1 pyramidal neurons causes a rapid, extracellular, population alkaline transient (PAT). It has been suggested that the plasma membrane Ca(2+)-ATPase (PMCA) is the source of this alkalinization, because it exchanges cytosolic Ca(2+) for external H(+). Evidence supporting this hypothesis, however, has thus far been inconclusive. We addressed this long-standing problem by measuring surface alkaline transients (SATs) from voltage-clamped CA1 pyramidal neurons in juvenile mouse hippocampal slices, using concentric (high-speed, low-noise) pH microelectrodes placed against the somata. In saline containing benzolamide (a poorly permeant carbonic anhydrase blocker), a 2-s step from -60 to 0 mV caused a mean SAT of 0.02 unit pH. Addition of 5 mM HEPES to the artificial cerebrospinal fluid diminished the SAT by 91%. Nifedipine reduced the SAT by 53%. Removal of Ca(2+) from the saline abolished the SAT, and addition of BAPTA to the patch pipette reduced it by 79%. The inclusion of carboxyeosin (a PMCA inhibitor) in the pipette abolished the SAT, whether it was induced by a depolarizing step, or by simulated, repetitive, antidromic firing. The peak amplitude of the "antidromic" SAT of a single cell averaged 11% of the PAT elicited by comparable real antidromic activation of the CA1 neuronal population. Caloxin 2A1, an extracellular PMCA peptide inhibitor, blocked both the SAT and PAT by 42%. These results provide the first direct evidence that the PMCA can explain the extracellular alkaline shift elicited by synchronous firing.
Makani
Sachin
S
Department of Physiology and Neuroscience, New York University Langone Medical Center, New York, New York 10016, USA.
Chesler
Mitchell
M
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D002478:Cells, Cultured; D045604:Extracellular Fluid / Q000737:chemistry / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D008297:Male; D051379:Mice; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism*; D017966:Pyramidal Cells / Q000737:chemistry* / Q000502:physiology*
D053499:Plasma Membrane Calcium-Transporting ATPases