Extracellular alkaline-acid-alkaline transients in the rat spinal cord evoked by peripheral stimulation.
Regional differences in extracellular pH (pHe) were found in unstimulated rat spinal cord using double-barrel pH-sensitive microelectrodes. The pHe in the lower dorsal horn (laminae III-VII) was about 7.15, i.e. by about 0.2 pH units lower than that measured in the cerebrospinal fluid. Transient acid shifts in pHe by 0.01-0.05 pH units were found when acute nociceptive stimuli (pinch, press, heat) were applied to the hind paw. Chemical or thermal injury evoked by subcutaneous injection of turpentine or by application of 1-3 ml of hot oil onto the hindpaw produced a long-term decrease in pHe base line in the lower dorsal horn by about 0.05-0.1 pH units. The decrease in pHe began 2-10 min after injury and persisted for more than 2 h. Electrical nerve stimulation (10-100 Hz, 20-60 s) elicited biphasic (acid-alkaline) or triphasic (alkaline-acid-alkaline) changes in pHe which have a similar depth profile as the concomitantly recorded increase in [K+]e. An initial alkaline shift by about 0.005 pH units was found to be significantly decreased by La3+, an H+ channel blocker. The dominating acid shift by about 0.1-0.2 pH units was accelerated and increased by acetazolamide (carbonic anhydrase inhibitor) showing that the high buffering capacity of the extracellular fluid may hamper the resolution of acid perturbations. Stimulation-evoked acid shifts were blocked by amiloride, SITS, DIDS and La3+ and therefore have a complex mechanism which includes Na+/H+ exchange, Cl-/HCO3- cotransport and/or Na+/Cl-/H+/HCO3- antiport and H+ efflux through voltage-sensitive H+ channels. The poststimulation alkaline shift (alkaline undershoot) was blocked by ouabain and reflects coupled clearance of K+ and H+ by active transport processes.
Syková
E
E
Institute of Physiological Regulations, Czechoslovak Academy of Sciences, Prague.
Svoboda
J
J
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D004558:Electric Stimulation; D005260:Female; D006863:Hydrogen-Ion Concentration; D010042:Ouabain / Q000494:pharmacology; D010525:Peripheral Nerves / Q000502:physiology*; D011188:Potassium / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D001639:Bicarbonates; D010042:Ouabain; D000086:Acetazolamide; D011188:Potassium