Influence of equinatoxin II on coronary smooth muscle membrane fluidity.

Equinatoxin II forms pores in artificial as well as in natural phospholipid bylayers. As it also reduces the perfusion through the coronary arteries it seemed reasonable to investigate the interaction of this protein with the plasmalemma of the vascular smooth muscle cells more directly with the patch-clamp method and with EPR using the spin probe methyl ester of 5-doxylpalmitate. In the EPR spectra at least three regions in the membranes were identified with different membrane fluidity. Application of 0.1 microM or 1 microM equinatoxin II increases the portion with the lower membrane fluidity, and irreversibly increases the unspecific membrane conductance. This is compatible with the view that equinatoxin II forms pores in the membrane bilayer.