Effects of repetitive stimulation, veratridine and ouabain on cytoplasmic pH in frog nerve fibres: role of internal Na+.
Changes of cytoplasmic pH (pHi) 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 pHi (by 0.015-0.06 pH units). Modification of Na+ channels by veratridine (VER, 10 microM) 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 pHi recovery after the termination of repetitive stimulation. A similar inhibition of post-stimulatory recovery of pHi 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 pHi. Li+ can be substituted for Na+ in this process.
Valkina
O N
ON
Uljanovsk State Pedagogic Institute, Moscow State University, Russian Federation.
Vergun
O V
OV
Turovetsky
V B
VB
Khodorov
B I
BI
D000818:Animals; D003593:Cytoplasm / Q000737:chemistry / Q000187:drug effects; D004558:Electric Stimulation; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009412:Nerve Fibers / Q000187:drug effects* / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology*; D011895:Rana ridibunda; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000187:drug effects; D014701:Veratridine / Q000494:pharmacology*
D010042:Ouabain; D014701:Veratridine; D000254:Sodium-Potassium-Exchanging ATPase