Modulation of N-Type Ca Channels by Intracellular pH in Chick Sensory Neurons

Kiss, Laszlo and Stephen J. Korn. Modulation of N-type Ca channels by intracellular pH in chick sensory neurons. J. Neurophysiol. 81: 1839–1847, 1999. Both physiological and pathological neuronal events, many of which elevate intracellular [Ca], can produce changes in intracellular pH of between 0.15 and 0.5 U, between pH 7.4 and 6.8. N-type Ca channels, which are intimately involved in exocytosis and other excitable cell processes, are sensitive to intracellular pH changes. However, the pH range over which N-type Ca channels are sensitive, and the sensitivity of N-type Ca channels to small changes in intracellular pH, are unknown. We studied the influence of intracellular pH changes on N-type calcium channel currents in dorsal root ganglion neurons, acutely isolated from 14-day-old chick embryos. Intracellular pH was monitored in patchclamp recordings with the fluorescent dye, BCECF, and manipulated in both the acidic and basic direction by extracellular application of NH4 1 in the presence and absence of intracellular NH4 . Changes in intracellular pH between 6.6 and 7.5 produced a graded change in Ca current magnitude with no apparent shift in activation potential. Intracellular acidification from pH 7.3 to 7.0 reversibly inhibited Ca currents by 40%. Acidification from pH 7.3 to pH 6.6 reversibly inhibited Ca currents by 65%. Alkalinization from pH 7.3 to 7.5 potentiated Ca currents by approximately 40%. Channels were sensitive to pHi changes with high intracellular concentrations of the Ca chelator, bis-(o-aminophenoxy)-N,N,N9,N9-tetraacetic acid, which indicates that the effects of pHi did not involve a Ca dependent mechanism. These data indicate that N-type Ca channel currents are extremely sensitive to small changes in pHi in the range produced by both physiological and pathological events. Furthermore, these data suggest that modulation of N-type Ca channels by pHi may play an important role in physiological processes that produce small changes in pHi and a protective role in pathological mechanisms that produce larger changes in pHi.