Mp. Sauviat et al., THE POLYETHER BISTRAMIDE-A AFFECTS THE CALCIUM SENSITIVITY OF THE CONTRACTILE PROTEINS IN FROG ATRIAL HEART-MUSCLE, Cell calcium, 14(4), 1993, pp. 301-309
The effects of Bistramide A, a new toxin isolated from the Urochordate
Lissoclinum bistratum Sluiter have been studied on the mechanical act
ivity of frog heart atrial muscle preparations. The peak tension of is
olated trabeculae was sensitive to nanomolar concentrations of Bistram
ide A. Lineweaver-Burk relationships suggest that Bistramide A compete
s with Ca for a common site. In voltage-clamped trabeculae, the toxin
inhibited both the cadmium-sensitive Ca current and the phasic compone
nt of the tension with a dissociation constant of 3.3 muM and a stoich
iometry of 2. Bistramide A decreased the isometric tension of skinned
fibres in a dose-dependent manner with a dissociation constant of 400
nM and a stoichiometry of 2. The toxin reduced the maximum Ca activate
d force and decreased the sensitivity of the contractile proteins to C
a. The data suggest that Bistramide A decreases the Ca-sensitivity of
contractile proteins prior to blocking the Ca current.