Endogenous DHP-sensitive Ca 2+ channels in Pleurodeles oocytes

Abstract

The double electrode voltage-clamp technique was used to study voltage-dependent Ca 2+ channels in Pleurodeles oocytes. From a holding potential of −80 mV, Ba-current ( I Ba) (recorded in Cl-free solution, Ba 2+ = 40 mM) activated at −36.7 ± 4 mV, peaked at −11.6 ± 4 mV and reversed at 55 ± 7 mV ( n = 24). This current activated slowly (rise time was 0.98 ± 0.2 s; n = 14 at −10 mV) and was not inactivated. Cadmium (Cd 2+, 500 μM) completely inhibited I Ba. The effect of Cd 2+ was dose-dependent (EC 50 = 37 ± 5 μM; n = 5). Moreover, I Ba was insensitive to ω-conotoxin (10 μM) but interestingly this I Ba. displayed dihydropyridine (DHP) sensitivity. Bay K 8644 (5 μM), a DHP activator, increased the peak current amplitude in a dose-dependent manner (EC 50 = 5.9 ± 0.6 μM; n = 10) and shifted the threshold and the maximum of current/voltage relationship towards negative potentials by − 10 mV. Nifedipine (5 μM), a DHP antagonist, decreased I Ba by 80% at HP of −80 mV (EC 50 = 1.2 ± 0.2 μM; n = 6). We concluded that Pleurodeles oocytes possess High-Voltage Activated Ca 2+ channels with properties similar to L-type Ca 2+ channels.