Circus-movement tachycardia in frog atrium monitored by voltage-sensitive dyes

Circus-movement tachycardia was studied using voltage-sensitive merocyanine-rhodanine dyes (dye XVII and NK2761). Excitatory waves were optically measured simultaneously from eight different regions of a ring of tissue formed from frog atrium. Application of acetylcholine in Ca2+-free solution (10(-10)-10(-9) g/ml) shortened the duration of optical action signals to cause nonuniform change in optical signal durations in about 60% of the preparations. Circus-movement tachycardia was produced by proper reduction and regional nonuniformity of optical signal durations. Under these circumstances it is easy to evoke circus-movement tachycardia by giving an extra stimulus to the site that shows a difference in optical signal durations.