Effects of a Lasiodora spider venom on Ca2+ and Na+ channels.
The venom of a Brazilian spider, Lasiodora sp (Mygalomorphae, Theraphosidae), was screened for activity against ion channels using Ca2+ imaging and whole-cell patch clamp in GH3 cells. When tetrodotoxin (TTX) was present to block Na+ channels, the venom abolished the Ca2+ oscillations that are normally present in these cells and reduced the basal level of intracellular Ca2+. Under patch clamp, the venom reduced the L-type Ca2+ channel conductance and caused a positive shift in its voltage dependence of activation. In addition to these effects, when applied without TTX, the venom also caused a slow and noisy increase in intracellular Ca2+. The sensitivity of this second effect to TTX suggested an effect on Na+ channels, which was tested using patch clamp. Control Na+ currents inactivated completely as a single exponential. Treatment with the venom did not affect the amplitude of I(Na), but caused it to divide in two slower exponential components plus a sustained component, all of which were suppressed by TTX. The venom also caused a negative shift in the voltage dependence of activation and steady-state inactivation of I(Na). The observed effects of this venom on whole-cell currents explain the changes it causes in intracellular Ca2+ in GH3 cells and demonstrate that the venom of this spider is a source of toxins active against ion channels.
Kushmerick
C
C
Departamento de Farmacologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. chris@icb.ufmg.br
Mesquita de Carvalho
F
F
de Maria
M
M
Massensini
A R
AR
Romano-Silva
M A
MA
Gomez
M V
MV
Kalapothakis
E
E
Prado
M A
MA
D000465:Algorithms; D001464:Barium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects*; D020746:Calcium Channels, L-Type / Q000187:drug effects; D002460:Cell Line; D005456:Fluorescent Dyes; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000187:drug effects*; D013111:Spider Venoms / Q000737:chemistry / Q000494:pharmacology*
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D005456:Fluorescent Dyes; D015222:Sodium Channels; D013111:Spider Venoms; D001464:Barium