Regulation of the miniature plasma membrane Ca2+ channel Imin by inositol 1,4,5-trisphosphate receptors

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.