sirolimus and 5--adenylyl-(beta-gamma-methylene)diphosphonate

Modulation of voltage-gated Ca(2+) channels controls activities of excitable cells. We show that high-voltage activated Ca(2+) channels are regulated by membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)) with different sensitivities. Plasma membrane PIP(2) depletion by rapamycin-induced translocation of an inositol lipid 5-phosphatase or by a voltage-sensitive 5-phosphatase (VSP) suppresses Ca(V)1.2 and Ca(V)1.3 channel currents by approximately 35% and Ca(V)2.1 and Ca(V)2.2 currents by 29% and 55%, respectively. Other Ca(V) channels are less sensitive. Inhibition is not relieved by strong depolarizing prepulses. It changes the voltage dependence of channel gating little. Recovery of currents from inhibition needs intracellular hydrolysable ATP, presumably for PIP(2) resynthesis. When PIP(2) is increased by overexpressing PIP 5-kinase, activation and inactivation of Ca(V)2.2 current slow and voltage-dependent gating shifts to slightly higher voltages. Thus, endogenous membrane PIP(2) supports high-voltage activated L-, N-, and P/Q-type Ca(2+) channels, and stimuli that activate phospholipase C deplete PIP(2) and reduce those Ca(2+) channel currents.

Topics: Adenosine Triphosphate; Barium; Biophysics; Calcium; Calcium Channels, L-Type; Cell Line, Transformed; Chelating Agents; Egtazic Acid; Electric Stimulation; Fluorescence Resonance Energy Transfer; Green Fluorescent Proteins; Humans; Immunosuppressive Agents; Ion Channel Gating; Membrane Potentials; Muscarinic Agonists; Oxotremorine; Patch-Clamp Techniques; Phosphatidylinositol 4,5-Diphosphate; Phosphoric Monoester Hydrolases; Sirolimus; Time Factors; Transfection