[Ca2+]i recordings and the inactivation of the high-voltage activated Ca2+ currents in the adult rat sensory neuron.
Fast, single cell, measurement of the average cytosolic [Ca2+]i with the Fura-2 technique suggests that the depolarization induced [Ca2+]i rise is entirely due to entry through the voltage-activated Ca2+ channels. Involvement of a Ca(2+)-induced Ca(2+)-release process is not evident. Under physiological cytosolic buffering the current-induced [Ca2+]i rise persists for seconds and decays exponentially (tau = 7 s). Analysis of the [Ca2+]i changes during two-pulse protocols indicates that the purely voltage-dependent inactivation of the high voltage-activated (HVA) channels, in the range -80/+70 mV, is a slow process (0.2-1 s) which removes at most 40% of the current. On the contrary, Ca(2+)-dependent inactivation acts in a fast way and it is therefore responsible for the fast inactivating phase of the current; this phase disappears under sustained [Ca2+]i loads, and reappears when redistribution of free Ca2+ takes place. A suitable correction may be devised to compensate for the Ca(2+)-dependent inactivation.
Peres
A
A
Dipartimento di Fisiologia e Biochimica Generali dell'Università di Milano, Italy.
Bertollini
L
L
Camagni
S
S
Wanke
E
E
D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D005246:Feedback; D016257:Fura-2 / Q000737:chemistry; D005724:Ganglia / Q000378:metabolism; D009475:Neurons, Afferent / Q000378:metabolism*; D051381:Rats; D013050:Spectrometry, Fluorescence; D013194:Staining and Labeling
D015220:Calcium Channels; D002118:Calcium; D016257:Fura-2