Absence of calcium channels in neonatal rat aortic myocytes

We have investigated whole-cell Ba²⁺ currents through Ca²⁺ channels (I_Ba) in single myocytes freshly isolated from the aortic media of neonatal (1-day-old) and adult (12-week-old) rats. In neonatal myocytes, I_Ba was undetectable even in presence of the dihydropyridine (DHP) agonist Bay K 8644. Binding of [³H]Nitrendipine on crude plasma membrane preparation of media confirmed the absence of DHP-receptors. By contrast, a robust DHP-sensitive ‘L-type’ I_Ba was recorded in adults which was consistent with the presence of specific [³H]Nitrendipine binding sites. In conclusion, neonatal aortic myocytes do not express any Ca²⁺ channels. The acquisition of L-type Ca²⁺ channels may be related to cell differentiation and acquisition of contractility during postnatal development.