Inactivation of single Ca2+ channels in rat sensory neurons by extracellular Ca2+.
1. Single Ca2+ channels conducting 20 mM Ba2+ from adult rat dorsal root ganglion cells were characterized using the two-electrode patch-clamp technique configuration. 2. Channels demonstrating specific characteristics of conductance, voltage dependence and dihydropyridine sensitivity were classified as high-threshold or L-type Ca2+ channels. 3. Mean single-channel current in 20 mM Ba2+ did not show inactivation, but inactivation occurred when using Ca2+ as a permeating ion. 4. Stimulus protocols were delivered alternately in the cell-attached and whole-cell electrode, while recording single-channel activity and total Ca2+ current simultaneously. 5. A mean single-channel Ba2+ current from a stimulated patch did not show inactivation. However, stimulation of a physiological whole-cell Ca2+ current induced a marked inactivation of mean single-channel Ba2+ current. 6. Complete Ca2+ current block by the addition of 200 microM Cd2+ in the external solution removed single-channel inactivation in patches stimulated through a whole-cell electrode.
Galli
A
A
Dipartimento di Fisiologia e Biochimica Generali, Università Statale di Milano, Italy.
Ferroni
A
A
Bertollini
L
L
Mazzanti
M
M
D000818:Animals; D001464:Barium / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D015640:Ion Channel Gating / Q000187:drug effects; D017736:Ion-Selective Electrodes; D008564:Membrane Potentials / Q000187:drug effects; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats
D015220:Calcium Channels; D002104:Cadmium; D001464:Barium; D000252:Calcium-Transporting ATPases; D002118:Calcium