Voltage-sensitive dyes. Discerning contraction and electrical signals in myocardium.

Muscle contraction can introduce artifact in attempted optical measurements of the action potential in heart tissue stained with voltage-sensitive dyes. Using rabbit sinus node and atrial tissue in vitro, we found that the voltage-sensitive part of the optical signal remains relatively unchanged by variations in the rate of external stimulation or by the application of transmural stimulation (TS), while the contraction-related component can be significantly increased by these same interventions. The relative contributions of membrane voltage and contraction to the optical signal can thus be determined. In particular, the rapid upstroke component of the action potential can be easily identified using this technique.