Negative chronotropic effect of botulinum toxin on neonatal rat cardiac myocytes.

We demonstrated that botulinum neurotoxin attenuated the spontaneous beating rate of cultured cardiac myocytes. Primary cultured cardiac myocytes were prepared from the ventricles of neonatal Wistar rats (1-3 days old). On 7 days after cell seeding, botulinum toxin type A incorporated into liposomes was added to the culture medium. At a final concentration of 5.0 micrograms/ml, botulinum toxin markedly attenuated the beating rate of cardiac myocytes within 2-4 hours. These results demonstrated the effect of SNARE-complex proteins on the spontaneous beating of cardiac myocytes.