Effects of repetitive stimulation, veratridine and ouabain on cytoplasmic pH in frog nerve fibres: role of internal Na +

Abstract

Changes of cytoplasmic pH (pH i) in frog nerve fibres during repetitive stimulation have been measured using the fluorescent pH indicator dye fluorescein diacetate (FDA). Under control conditions repetitive (10–50 Hz) stimulation caused only a very small decrease in pH i (by 0.015–0.06 pH units). Modification of Na + channels by veratridine (VER, 10, μM) greatly increased this stimulus-evoked (SE) internal acidification. Blockade of the Na +-K + pump by ouabain (0.5 mM) enhanced the effects VER and prevented pH i recovery after the termination of repetitive stimulation. A similar inhibition of post-stimulatory recovery of pH i was observed after replacement of external Na + with Li +, which is not accepted by the Na +-K + pump instead of Na +. These data suggest that SE intracellular acidification in nerves results from or is closely associated with an increase in [Na +] i. Treatments that promote Na + influx and accumulation of Na + inside the fibre enhance reduction of pH i. Li + can be substituted for Na + in this process.