RESUMO
In order to obtain some evidences of the role of parathyroid hormone (PTH) in regulating calcium metabolism, and explore the mechanisms by which PTH regulates calcium in the heart, 45Ca was used to study the influence of bovine PTH1-34 fragment (bPTH1-34) on calcium transsacolemma. The results indicate that bPTH1-34(l?I0-7mol ? L-1) increases beating rate of heart cells under normal state and it markedly increases the rapid (5 min) and the slow (120 min) phases of 45Ca influx in heartcells (under normal, KC1 10-5 mol?L-1 high K+depolarised, NA 10-7mol?L-1receptors activated states), but it could also reduce 45Ca efflux from the cultured heart cells. It suggests that the mechanisms caused by bPTH1-34 which enhances the cytosolic calcium concentration and myocardial beating rate may be related with cAMP level elevated in heart cells.
RESUMO
At the concentrations of 10-8mol/L, 5.5?l0-8mol/L, 10-7mol/L morphine produced a dose-dependent increase of beating rate in cultured rat heart cells with 9%,32%and 81% respectively. The increase was antagonized by opiate antagonist naloxone ( 10-5mol/L ) , but not affected by propranolol ( 10-5mol/L ) which could cancel the positive chronotropy of isoprenaline ( 10-9mol/L ) on the beating cells. The results support the concept that morphine may be a direct effect on myocadium, perhaps through opiate receptors.