Nickel is a highly versatile metal that is used in numerous applications including electrical vehicle batteries, alloys, electroplating and as a source of electrical power. It is a highly corrosion and oxidation resistant metal with excellent thermal conductivity and an abundance of ductile properties.
The effects of nickel on voltage-activated calcium channels are complex, and different subtypes and combinations of beta subunits exhibit differential sensitivity to Ni2+ block. Using cloned alpha1A (a1A), a1B, a1C and a1E voltage-activated channels transiently expressed in Xenopus oocytes, we investigated the sensitivity of these channels to Ni2+ block.
Inhibition of a1C and a1E currents was accompanied by reduction of the maximum slope conductance, while a1A and a1B currents were shifted toward more depolarized potentials. Dose-response curves of current-inhibition with nickel were fitted to the Hill equation: B = (1 + IC50/(Ni2+)n)-1.
HGGG/E137Q and HGGG/H191Q currents were also sensitively blocked by low concentrations of nickel. The IC50 values of these channels were 5.1 +- 1.2 mm and 312.5 +- 4.2 mm, respectively.
Cav3.1 and HHHH channel currents were inhibited by serial doses of nickel to a test potential to -20 mV from a holding potential of -90 mV every 15 s (Fig. 1 A, B, C and D). Typical currents were superimposed and normalized to the peak value in the absence of Ni2+, then dose-response curves were fit to the data with the Hill equation.
These results indicate that structural determinants for the nickel-sensitive GGGG and HHGG channels reside between the amino terminus of IS4 and IS4. These regions are only 15% identical to HVA a1 subunits at the amino acid level, suggesting that they must be important structural elements that bind Ni2+.