DEVELOPMENT OF INWARDLY RECTIFYING K+ CHANNEL FAMILY IN RAT VENTRICULAR MYOCYTES

The ATP-sensitive K+ current (I-K,I-ATP), the inward rectifier K+ curr ent (I-K1), and the acetylcholine-activated K+ current (I-K,I-ACh) wer e recorded in fetal, neonatal, and adult rat ventricular myocytes usin g the patch-clamp technique. The density (pA/pF) of I-K1 increased fro m gestation day 10 through neonatal day 1 and then decreased after neo natal day 30. The density of I-K,I-ATP activated maximally by metaboli c inhibition changed in parallel with the I-K1 density, and the densit y of I-K,I-ATP channel distribution was 1.3 times higher than that of I-K1 throughout the development. We failed to observe developmental ch anges in the single-channel conductance and the mean open time of I-K1 and I-K,I-ATP channels. However, the open probability of the I-K,I-AT P channel was lower in fetuses, and the sensitivity to ATP was highest in 1-day neonates. I-K,I-ACh were present in the ventricle at all sta ges of development but at a much lower density than in atrium. The rel ationship between the resting membrane potential and the development o f the inwardly rectifying K+ channel family is discussed.