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.