We have investigated whole-cell Ba2+ currents through Ca2+ channels (I
-Ba) in single myocytes freshly isolated from the aortic media of neon
atal (1-day-old) and adult (12-week-old) rats. In neonatal myocytes, I
-Ba was undetectable even in presence of the dihydropyridine (DHP) ago
nist Bay K 8644. Binding of [H-3]Nitrendipine on crude plasma membrane
preparation of media confirmed the absence of DHP-receptors. By contr
ast, a robust DHP-sensitive 'L-type' I-Ba was recorded in adults which
was consistent with the presence of specific [H-3]Nitrendipine bindin
g sites. In conclusion, neonatal aortic myocytes do not express any Ca
2+ channels. The acquisition of L-type Ca2+ channels may be related to
cell differentiation and acquisition of contractility during postnata
l development.