Modulation of Ca 2+ Influx in Leech Retzius Neurons. I. Effect of Extracellular pH

Abstract

We investigated the cytosolic free Ca2+ concentration ([Ca2+]i) of leech Retzius neurons in situ while varying the extracellular and intracellular pH as well as the extracellular ionic strength. Changing these parameters had no significant effect on [Ca2+]i when the membrane potential of the cells was close to its resting value. However, when the cells were depolarized by raising the extracellular K+ concentration or by applying the glutamatergic agonist kainate, extracellular pH and ionic strength markedly affected [Ca2+]i, whereas intracellular pH changes appeared to have virtually no effect. An extracellular acidification decreased [Ca2+]i, while alkalinization or reduction of the ionic strength increased it. Correspondingly, [Ca2+]i also increased when the kainate-induced extracellular acidification was reduced by raising the pH-buffering capacity. At low extracellular pH, the membrane potential to which the cells must be depolarized to evoke a detectable [Ca2+]i increase was shifted to more positive values, and it moved to more negative values at high pH. We conclude that in leech Retzius neurons extracellular pH, but not intracellular pH, affects [Ca2+]i by modulating Ca2+ influx through voltage-dependent Ca2+ channels. The results suggest that this modulation is mediated primarily by shifts in the surface potential at the extracellular side of the plasma membrane.

The Effects of pH on Beta-Endorphin and Morphine Inhibition of Calcium Transients in Dorsal Root Ganglion Neurons

“…nels. 15,26 Despite the opposing influence of acidic pH on the magnitude of capsaicin-and high-K ϩ -induced calcium responses, we showed that opioid inhibition of these responses was mutually enhanced by acidic pH. This supports the conclusion that protons modulated opioid receptor-mediated inhibition and did not simply affect stimuli intensity.…”

Extracellular pH Modifies Mitochondrial Control of Capacitative Calcium Entry in Jurkat Cells

“…29). Similar dependencies between extracellular pH and Ca 2ϩ entry were found in rabbit-resident alveolar macrophages, neurons, and pancreatic cells (23,30,31). The results presented in this study not only correspond well to these data but also indicate a novel mechanism connecting both extracellular pH and mitochondrial effects on CCE in Jurkat cells.…”

Ionic mechanism of ouabain-induced swelling of leech Retzius neurons

“…The ouabain-induced [Ca 2+ ] i increase will be due to the activation of voltage-dependent Ca 2+ channels (see [24]), but it is unclear why [Ca 2+ ] i recovered although the membrane depolarization persisted and why it often increased again after ouabain washout. It is only noted that the activity of the voltage-dependent Ca 2+ channels in Retzius neurons is strongly affected by the extracellular pH and the extracellular Ca 2+ concentration [25,26] and that due to the Ca 2+ affinity of gluconate, the extracellular Ca 2+ concentration of the Cl − -free solution was distinctly lower than that of the physiological solution (see [39]). A contribution of Na + -Ca 2+ exchange to the observed [Ca 2+ ] i changes can be excluded because in Retzius neurons, [Ca 2+ ] i is independent of extracellular Na + ( [23,24]; see Fig.…”