Contrasting effects of Cd2+ and Co2+ on the blocking/unblocking of human Cav3 channels.
Inorganic ions have been used widely to investigate biophysical properties of high voltage-activated calcium channels (HVA: Ca(v)1 and Ca(v)2 families). In contrast, such information regarding low voltage-activated calcium channels (LVA: Ca(v)3 family) is less documented. We have studied the blocking effect of Cd2+, Co2+ and Ni2+ on T-currents expressed by human Ca(v)3 channels: Ca(v)3.1, Ca(v)3.2, and Ca(v)3.3. With the use of the whole-cell configuration of the patch-clamp technique, we have recorded Ca2+ (2 mM: ) currents from HEK-293 cells stably expressing recombinant T-type channels. Cd2+ and Co2+ block was 2- to 3-fold more potent for Ca(v)3.2 channels (EC50 = 65 and 122 microM, respectively) than for the other two LVA channel family members. Current-voltage relationships indicate that Co2+ and Ni2+ shift the voltage dependence of Ca(v)3.1 and Ca(v)3.3 channels activation to more positive potentials. Interestingly, block of those two Ca(v)3 channels by Co2+ and Ni2+ was drastically increased at extreme negative voltages; in contrast, block due to Cd2+ was significantly decreased. This unblocking effect was slightly voltage-dependent. Tail-current analysis reveals a differential effect of Cd2+ on Ca(v)3.3 channels, which can not close while the pore is occupied with this metal cation. The results suggest that metal cations affect differentially T-type channel activity by a mechanism involving the ionic radii of inorganic ions and structural characteristics of the channels pore.
Díaz
D
D
Departamento de Biofisica, Instituto de Fisiologia Celular, Universidad Nacional Autonoma de Mexico, Mexico City, DF, 04510, Mexico.
Bartolo
R
R
Delgadillo
D M
DM
Higueldo
F
F
Gomora
J C
JC
D002104:Cadmium / Q000737:chemistry / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D003035:Cobalt / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D009532:Nickel / Q000737:chemistry / Q000502:physiology; D018408:Patch-Clamp Techniques
C479952:CACNA1H protein, human; D020747:Calcium Channels, T-Type; D002104:Cadmium; D003035:Cobalt; D009532:Nickel