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.
Departamento de Biofisica, Instituto de Fisiologia Celular, Universidad Nacional Autonoma de Mexico, Mexico City, DF, 04510, Mexico.
D
D
Díaz
R
R
Bartolo
D M
DM
Delgadillo
F
F
Higueldo
J C
JC
Gomora
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