TEMPERATURE-DEPENDENCE OF MULTIPLE HIGH-VOLTAGE ACTIVATED CA2+ CHANNELS IN CHICK SENSORY NEURONS

The temperature dependence of high voltage activated Ca2+ channels has been investigated in cultured dorsal root ganglion neurones from chic k embryos, using the cell-attached patch-clamp technique. The dihydrop yridine sensitive L-type Ca2+ channel had a conductance of 23 pS, with 110 mM Ba2+ as charge carrier and in the presence of 3 mu M Bay K 864 4. When the temperature was raised from 15 to 30 degrees C, the unitar y channel current amplitude increased, with Q(10) value equal to 1.4. The rising phase of the averaged single-channel current became faster, with Q(10) value 2.7, whereas the decay phase showed a lower temperat ure sensitivity. Channel open probability decreased according to an ex ponential distribution of open and closed times. A second type of Ca2 channel was identified, which was DHP-insensitive and had a lower con ductance with a mean value equal to 13 pS. For the current amplitude, the Q(10) value was 1.3. Both activation and inactivation kinetics wer e strongly accelerated by an increase in temperature. The correspondin g time constants gave Q(10) values equal to 5.9 for activation, and 2. 0 for inactivation. Peak channel open probability was highly sensitive to a change in temperature, with a Q(10) value of 1.6. Finally, in om ega-conotoxin GVIA pre-treated neurones, a non-inactivating DHP-insens itive Ca2+ channel with the lowest unitary conductance (10 pS) and a m uch lower temperature dependence was recorded. Single-channel current was increased by heating, with Q(10) value 1.3, whereas the channel ki netics were almost unaffected by temperature. Our data are consistent with the assumption that the different temperature dependence of the C a2+ channel behaviours may be explained by separate gating processes o f three types of Ca2+ channels.