Evidence for roles of the activating function in electric stimulation

The hypothesis that the activating function drives transmembrane voltage changes (Delta V-m) has been tested in hearts. Optical Delta V-m were measured during activating functions produced with nonuniform and uniform transparent electrodes. When a nonuniform electrode was used to produce partial derivative(2)V(e)/partial derivative x(2), the signs of Delta V-m and partial derivative(2)V(e)/partial derivative x(2) matched. The extracellular voltage gradients, often assumed important, did not predict Delta V-m. When a uniform electrode was used to eliminate partial derivative(2)V(e)/partial derivative x(2), the signs of PV, matched the signs of (as,la)(av,la) estimated from variations in heart width, Demonstration of the activating function as a determinant of stimulation may improve research and therapy that use electric stimulation.