Regulation of the miniature plasma membrane Ca2+ channel I(min) by inositol 1,4,5-trisphosphate receptors

Abstract

I(min) is a plasma membrane-located, Ca2+-selective channel that is activated by store depletion and regulated by inositol 1,4,5-trisphosphate (IP3). In the present work we examined the coupling between I(min) and IP3 receptors in excised plasma membrane patches from A431 cells. I(min) was recorded in cell-attached mode and the patches were excised into medium containing IP3. In about 50% of experiments excision caused the loss of activation of I(min) by IP3. In the remaining patches activation of I(min) by IP3 was lost upon extensive washes of the patch surface. The ability of IP3 to activate I(min) was restored by treating the patches with rat cerebellar microsomes reach in IP3 receptors but not by control forebrain microsomes. The re-activated I(min) had the same kinetic properties as I(min), when it is activated by Ca2+mobilizing agonists in intact cells and by IP3 in excised plasma membrane patches and it was inhibited by the I(crac) inhibitor SKF95365. We propose that I(min) is a form of I(crac) and is gated by IP3 receptors.