Phosphatidylinositol-4,5-bisphosphate modulates activity of receptor-induced calcium entry channels in A431 cells

Using patch clamp technique, we investigated the influence of anti-phosphatidylinositol-4,5-bisphosphate antibody (PIP₂Ab) and phosphatidylinositol-4,5-bisphosphate (PIP₂) on the activity of inositol-1,4,5-trisphosphate (IP₃)-dependent miniature calcium channels (I_min) in plasma membrane of human carcinoma A431 cells. We demonstrate here that I_min activity is greatly enhanced in the presence PIP₂Ab and diminished in the presence of PIP₂. Anti-PIP₂ antibodies induce more than a 6-fold increase in I_min sensitivity to IP₃ activation and almost 4-fold change in I_min maximal open probability. We further demonstrated the synergism in activation of I_min by extracellular UTP and intracellular IP₃. UTP receptor stimulation of PLC leads to ane increase in I_min sensitivity to IP₃ as well to anti-PIP₂ antibody. Based on these and previous data, we concluded that I_min/IP₃R complex exists, and complex activation is modulated by PIP₂. The activation of endogenous PLC and, consequently, the decrease of PIP₂ level induced by Ca²⁺-mobilizing agonist diminish the inhibitory effect of PIP₂ on I_min/IP₃R complex and increase the ability of IP₃ to activate I_min.