Submitted on December 2, 2005
Accepted on July 19, 2006
Relationships between calcium and pH in the regulation of the slow afterhyperpolarization in cultured rat hippocampal neurons
Tony Kelly1 and John Church1*
1 Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada
* To whom correspondence should be addressed. E-mail: jchurch{at}interchange.ubc.ca.
The Ca2+-dependent slow afterhyperpolarization (AHP) is an important determinant of neuronal excitability. Although modest changes in extracellular pH (pHo) are known to modulate the slow AHP, the relative contributions of changes in the priming calcium signal and intracellular pH (pHi) to this effect remain poorly defined. To gain a better understanding of the modulation of the slow AHP by pHo, we performed simultaneous recordings of intracellular free calcium concentration ([Ca2+]i), pHi, and the slow AHP in cultured hippocampal neurons co-loaded with the Ca2+- and pH-sensitive fluorophores fura-2 and SNARF-5F, respectively, and patch-clamped using the perforated patch technique. Decreasing pHo from 7.2 to 6.5 lowered pHi, reduced depolarization-evoked [Ca2+]i transients and inhibited the subsequent slow AHP; opposite effects were observed when pHo was increased from 7.2 to 7.5. Although decreases and increases in pHi (at a constant pHo) reduced and augmented, respectively, the slow AHP in the absence of marked changes in preceding [Ca2+]i transients, the inhibition of the slow AHP by decreases in pHo was correlated with low pHo-dependent reductions in [Ca2+]i transients rather than the decreases in pHi that accompanied the decreases in pHo. In contrast, high pHo-induced increases in the slow AHP were correlated with the accompanying increases in pHi rather than high pHo-dependent increases in [Ca2+]i transients. The results indicate that changes in pHo modulate the slow AHP in a manner that depends on the direction of the pHo change and substantiate a role for changes in pHi in modulating the slow AHP during changes in pHo.
