Regulation of cardionatrin on beating rate of cultured myocardial cells of neonatal rats

The 2-10 d cultured myocardial cells of Wistar neonatal rats were used. Isoproterenol accelerated the beats per min (bpm) of cultured myocardial cells. Propranolol slowed down the bpm. Cardionatrin 192 pg/ml increased the bpm when its original rate was below 100 min-1 and decreased the bpm as the rate was over 100 min-1. Cardionatrin 1920 pg/ml induced the similar but weaker effect. These phenomena suggest the existence of negative feedback endocrine loop of cardionatrin in the cultured myocardial cells.
Propranolol decreased the beating rates independently of the original rate. Cardionatrin reversed the effects of rhomotoxin (increased rate) and propranolol (decreased rate). These results suggest that cardionatrin is a regulator of the heart rate.