Endogenous DHP‐sensitive Ca²⁺ channels in Pleurodeles oocytes

Abstract

The double electrode voltage-clamp technique was used to study voltage-dependent Ca*' channels in Pleurodeles oocytes. From a holding potential of -80 mV, Ba-current (ZBa) (recorded in Cl-free solution, Ba 2+ = 40 mM) activated at -36.7 + 4 mV, peaked at -11.6 f 4 mV and reversed at 55 + 7 mV (n = 24). This current activated slowly (rise time was 0.98 f 0.2 s; n = 14 at -10 mV) and was not inactivated. Cadmium (Cd", 5OOpM) completely inhibited I,,. The effect of Cd2+ was dose-dependent (ECSo = 37 + 5pM; n = 5). Moreover, ZBa was insensitive to w-conotoxin (10pM) but interestingly this ZBa displayed dihydropyridine (DHP) sensitivity. Bay K 8644 (SpM), a DHP activator, increased the peak current amplitude in a dose-dependent manner (EC,,, = 5.9 f 0.6 PM; n = 10) and shifted the threshold and the maximum of current/voltage relationship towards negative potentials by -10 mV. Nifedipine (5 PM), a DHP antagonist, decreased Z,, by 80% at HP of -80 mV (EC,, = 1.2 + 0.2 PM; n = 6). We concluded that Pleurodeles oocytes possess High-Voltage Activated Ca" channels with properties similar to L-type Ca" channels.

Meiosis reinitiation in Ruditapes philippinarum (Mollusca): involvement of L-calcium channels in the release of metaphase I block

“…Similar results are found in ascidian oocytes and eggs (Dale et al, 1991). In vertebrates, L-type calcium channels are expressed also in the oocytes of the amphibian Pleurodeles zvaltl (Ouadid et al, 1994).…”

Voltage-gated calcium channels inPleurodelesoocytes: classification, modulation and functional roles

“…Two kinds of Ca 2+ channel activity were recorded: the previously described L-type (Ouadid et al, 1994) and a transient one that has never been shown before (Ouadid, 1996). Furthermore, during the resting season, the transient-type Ca 2+ channel seems to be predominant since some batches of oocytes did not display the L-type channel.…”

Expression of a rapidly inactivating Ca2+ channel in Pleurodeles oocytes during the resting season

“…The present study demonstrated that, in addition to the known L-type Ca 2+ channel [7], Pleurodeles oocytes express a transient Ca 2+ channel activity during the resting season, i.e. when maturation does not naturally occur.…”

“…Oocytes were dissected away from ovaries of female Pleurodeles wahlii (urodele amphibian, from Laboratoire de Physiologie Cellulaire, SN3, USTL) anesthetized with 1% MS 222 (tricaine methanesulfonate, Sandoz) and prepared as previously reported [7]. Stage VI oocytes were selected for electrophysiological measurements.…”

“…Both T-type (a fast transient component activated at low potential; LVA) and L-type (a slow component activated at high potential; HVA) have been reported in starfish Mediaster aequalis oocytes [4], ascidian Ciona intestinalis oocytes and eggs [5,6]. Recently, we have described a HVA Ca 2+ channel which has been attributed to the L-type on the basis of to its kinetics and pharmacological properties in Pleurodeles oocytes [7]. Interestingly, only the L-type current was observed during the breeding season.…”