Intracellular acidification is associated with changes in free cytosolic calcium and inhibition of action potentials in rat trigeminal ganglion.
The effect of intracellular acidification and subsequent pH recovery in sensory neurons has not been well characterized. We have studied the mechanisms underlying Ca(2+)-induced acidification and subsequent recovery of intracellular pH (pH(i)) in rat trigeminal ganglion neurons and report their effects on neuronal excitability. Glutamate (500 μM) and capsaicin (1 μM) increased intracellular Ca(2+) concentration ([Ca(2+)](i)) with a following decrease in pH(i). The recovery of [Ca(2+)](i) to the prestimulus level was inhibited by LaCl(3) (1 mM) and o-vanadate (10 mM), a plasma membrane Ca(2+)/ATPase (PMCA) inhibitor. Removal of extracellular Ca(2+) also completely inhibited the acidification induced by capsaicin. TRPV1 was expressed only in small and medium sized trigeminal ganglion neurons. mRNAs for Na(+)/H(+) exchanger type 1 (NHE1), pancreatic Na(+)-HCO(3)(-) cotransporter type 1 (pNBC1), NBC3, NBC4, and PMCA types 1-3 were detected by RT-PCR. pH(i) recovery was significantly inhibited by pretreatment with NHE1 or pNBC1 siRNA. We found that the frequency of action potentials (APs) was dependent on pH(i). Application of the NHE1 inhibitor 5'-(N-ethyl-N-isopropyl) amiloride (5 μM) or the pNBC1 inhibitor 4',4'-di-isothiocyanostilbene-2',2'-sulfonic acid (500 μM) delayed pH(i) recovery and decreased AP frequency. Simultaneous application of 5'-(N-ethyl-N-isopropyl) amiloride and 4',4'-di-isothiocyanostilbene-2',2'-sulfonic acid almost completely inhibited APs. In summary, our results demonstrate that the rise in [Ca(2+)](i) in sensory neurons by glutamate and capsaicin causes intracellular acidification by activation of PMCA type 3, that the pH(i) recovery from acidification is mediated by membrane transporters NHE1 and pNBC1 specifically, and that the activity of these transporters has direct consequences for neuronal excitability.
Department of Physiology, School of Dentistry, Seoul National University and Dental Research Institute, Yeongeondong 28, Chongnoku, Seoul 110-749, Korea.
Sung-Min
SM
Hwang
Na-Youn
NY
Koo
Meihong
M
Jin
Alexander J
AJ
Davies
Gae-Sig
GS
Chun
Se-Young
SY
Choi
Joong-Soo
JS
Kim
Kyungpyo
K
Park
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002211:Capsaicin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D049990:Membrane Transport Modulators / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018689:Sensory System Agents / Q000494:pharmacology; D027982:Sodium-Bicarbonate Symporters / Q000037:antagonists & inhibitors / Q000378:metabolism; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D012668:Trigeminal Ganglion / Q000166:cytology / Q000378:metabolism*
D004791:Enzyme Inhibitors; D049990:Membrane Transport Modulators; D018689:Sensory System Agents; C452850:Slc9a1 protein, rat; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D018698:Glutamic Acid; D053499:Plasma Membrane Calcium-Transporting ATPases; D002211:Capsaicin; D002118:Calcium