Development of the Action Potential of the Prenatal Rat Heart

Abstract

Transmembrane action potentials were recorded from embryonic rat hearts at ages between 10& days of gestation and birth (21 to 22 days). The resting potential averaged 30 to 40 mv at IOJ2 days and increased to around 80 mv by birth. Two periods of rapid increase in resting potential were noted: 1) from 10^ to 13& days and 2) from 19M days of gestation to birth. The maximal upstroke velocity of the action potential increased as the resting potential increased. The duration of the ventricular and atrial action potentials was inversely related to heart rate, and their rate sensitivity decreased with age. The atrial action potential lost its rate sensitivity by 13M days of gestation and the ventricular action potential lost its by birth. At IOJ2 days diastolic depolarization was found in the area of the ventricle proximate to the A-V junction, the left and right atria, and the sinus venosus. The velocity of the diastolic depolarization was greatest in the sinus venosus and least in the ventricle. The diastolic depolarization decreased with growth and was lost by 13/2 days of gestation. ADDITIONAL KEY WORDScardiac action potentials cardiac pacemaker cardiac electrophysiology diastolic depolarization mammalian embryonic heart growth and differentiation• The transmembrane action potential of the embryonic and fetal heart has been studied principally in the chick embryo (1-7).In the ventricle of 6-to 8-day chick embryo hearts, Lehmkuhl and Sperelalcis (2) found resting potentials of 72 mv and action potentials of 86 mv. Potentials in the range of 30 to 50 mv were found in 37-to 67-hour chick embryos by Meda and Ferroni (3). Action potential configuration was found to be simi-

Correlation of the glycoside response, the force staircase, and the action potential configuration in the neonatal rat heart.

“…Bernard and Gargouil (7) and Couch et al (8) have demonstrated an increasing resting potential and a decreasing action potential duration from 10 days gestation to birth (21 days). Iri addition, Bernard and Gargouil (7) have shown that at 10 days gestation the action potential amplitude and configuration are insensitive to tetrodotoxin at concentrations as high as 10"…”

Organization and Fine Structure of a Pacemaker Derived from Fetal Rat Myocardium

“…Pacemaker precursor cells have been identified in the ventricular primordia of the chick heart (stage 4, 18-19 h of incubation) (17). Transmembrane potentials of all myocardial cells at this developmental stage and later depolarize spontaneously during diastole (14,(18)(19)(20). As development proceeds, spontaneous depolarization is observed in progres- sively fewer myocardial cells (3,(19)(20)(21).…”

Changes in α1‐adrenoceptor coupling to Ca2+ channels during development in rat heart

“…Therefore, it is very likely that the a,-adrenoceptors are coupled to Ca" channels at an early stage of development and then shift to the Z, in the mature state. Another point is that ventricular myocytes from prenatal and newborn rats have an action potential with an elevated plateau similar to that of other mammalian species [21], while the action potential in adult rat ventricular cells has a duration of less than 100 ms [l]. The duration of the action potential is in part due to the influence of Ca".…”