Ca2+ efflux mechanisms following depolarization evoked calcium transients in cultured rat sensory neurones.
1. We have used a combination of microfluorimetry and patch-clamp techniques to investigate cytoplasmic Ca2+ ([Ca2+]i) buffering in response to physiological Ca2+ loads in neurones cultured from the dorsal root ganglia of the rat. 2. In cells loaded with Indo-1 AM and using high resistance microelectrodes to initiate and record action potentials, single action potentials were associated with a measurable rise in [Ca2+]i. Short trains of action potentials evoked [Ca2+]i transients with monoexponential recovery rates with time constants of around 5 s. 3. Similar Ca2+ buffering properties were seen in cells perfused with patch-clamp pipettes in the whole-cell recording mode suggesting that the slow (seconds) Ca2+ buffering properties were not seriously perturbed by the recording technique. 4. In cells held under voltage clamp, reversal of the Na(+)-Ca2+ exchanger driving force had a small but significant effect on the rate of Ca2+ removal. 5. Increasing extracellular pH or adding vanadate (200 microM) to the internal solution dramatically slowed the rate of recovery. Addition of calmidazolium to the pipette solution also produced a significant but much less dramatic slowing of Ca2+ efflux. 6. The results demonstrate that the activity of a plasmalemmal Ca(2+)-ATPase is important for the removal of somatic Ca2+ loads of a similar amplitude to those generated by the firing of a few action potentials.
Benham
C D
CD
Department of Pharmacology, Smith, Kline & French Research Ltd., Welwyn, Herts.
Evans
M L
ML
McBain
C J
CJ
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002110:Caffeine / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D009475:Neurons, Afferent / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011930:Reaction Time; D012964:Sodium / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007093:Imidazoles; D002110:Caffeine; D014638:Vanadates; C031938:calmidazolium; D012964:Sodium; D002118:Calcium