Ligand-Activated Ca²⁺ Channels in the Nuclear Envelope of Starfish Oocytes

Abstract

The regulation of the calcium pool in the cell nucleus is a controversial issue. The presence in the envelope of large pores has often been taken as an indication for the free and unhindered traffic of Ca²⁺ between the cytoplasm and the nucles. Accordingly, experiments in a number of Laboratories, especially with nuclear targeted fluorescent indicators (Brini et al., 1993; Allbritton et al., 1994) have detected insignificant delays in the transmission of cytosolic Ca²⁺ waves to the cytoplasm. Others, however, have measured significant delays even using essentially the same methods (Badminton et al., 1995). In addition, patch-clamp work on nuclear envelopes have shown giga-ohm resistance, and single channel activity, despite the presence of dozens of pores in the patch (Mazzanti et al., 1990; Dale et al., 1994; Santella & Kyozuka, 1994; Santella, 1996). Very likely, then, the nuclear pores exist in both Ca²⁺ impermeant and Ca²⁺ permeant states: a mechanism for the gating on the pores based on the state of depletion of the envelope Ca²⁺ store has been recently proposed (Greber & Gerace, 1995; Stehno-Bittel et al., 1995).