Résumé
T-type Ca
2+
channels have been suggested to play a role in cardiac automaticity, cell growth, and cardiovascular remodeling. Although three genes encoding for a T-type Ca
2+
channel have been identified, the nature of the isoform(s) supporting the cardiac T-type Ca
2+
current ( I
Ca,T
) has not yet been determined. We describe the postnatal evolution of I
Ca,T
density in freshly dissociated rat atrial and ventricular myocytes and its functional properties at peak current density in young atrial myocytes. I
Ca,T
displays a classical low activation threshold, rapid inactivation kinetics, negative steady-state inactivation, slow deactivation, and the presence of a window current. Interestingly, I
Ca,T
is poorly sensitive to Ni
2+
and insensitive to R-type current toxin SNX-482. RT-PCR experiments and comparison of functional properties with recombinant Ca
2+
channel subtypes suggest that neonatal I
Ca,T
is related to the α
1G
-subunit. Atrial natriuretic factor (ANF) secretion was measured using peptide radioimmunoassays in atrial tissue. Pharmacological dissection of ANF secretion indicates an important contribution of I
Ca,T
to Ca
2+
signaling during the neonatal period.