Inositol 1,4,5-trisphosphate activates two types of Ca 2+-permeable channels in human carcinoma cells

Ca 2+-permeable channels in human carcinoma A431 cells were studied using the patch clamp technique. We have found two types of Ca 2+-penneable channels which are activated by inositol 1,4,5-trisphosphate (IP 3) applied to the intracellular side of the plasma membrane. Unitary conductances of these channels are 3.7 and 13 pS (105 mM Ca 2+in recording pipette, 30–33°C). From the extracellular side of the membrane the channels are activated by EGF. It is assumed that extracellular agonists open both channel types by stimulating the release of IP 3from the membrane.