Phosphatidylinositol 4,5-Bisphosphate-induced Ca2+ Release from ...

Vol. 266, No. 12, Issue of April 25, pp. 7699-7705, 1991 Printed in U.S.A.

THEJOURNALOF BIOLOGICAL CHEMISTRY 0 1991 by The American Society for Biochemistry and Molecular Biology, Inc.

Phosphatidylinositol 4,5-Bisphosphate-inducedCa2+ Release from Skeletal Muscle Sarcoplasmic Reticulum Terminal Cisternal Membranes Ca2+FLUX AND SINGLECHANNELSTUDIES* (Received for publication, November 19, 1990)

Alice ChulQlI and EnricoStefaniII From the $Section of Cardiovascular Sciences, Department of Medicine and 11 Department of Molecular Physiology and Biophysics, Baylor College of Medicine and the §Methodist Hospital, Houston, Texas 77030

We report here that the inositol1,4,5-trisphosphate a stimulatory factor in excitation-contraction (E-C) coupling (IP3)precursor, L-a-phosphatidylinositol4,5-bisphos- has been examined. However, the role of IP3in skeletal muscle phate (PIP2)is a potent molecule(1 PM) which activates E-C coupling is not clear (3). the ryanodine-sensitive Caz+ release channel from rab- Other inositol derivatives in the biosynthetic pathway, tetbit skeletal muscleterminal cisternae incorporated rakisphosphates andcyclic triphosphates, have also been suginto a phospholipid bilayer. It alsostimulatesCaz+ gested to play roles as second messengers in other cell types release from these membrane vesicles. Therefore, it (4).Recently, the IP3precursor, PIP2,has been demonstrated may play a modulating role in excitation-contraction to elicit Caz+ release from nonmuscle tissue (5) and crude coupling. "heavy" SR membranes of skeletal muscle (6, 7). We proceed In the bilayer, PIPz added on the cytoplasmic side increased themean channel opening probability 2-12- to investigate the efficacy of PIP2 versus IP, on the skeletal muscle SRCa2+ release channel by incorporating purified fold in the presence and absence of physiological Mg2+ andATP. From flux studies, PIPz-induced Caz+ re- junctional terminal cisternal membranes into bilayers and to lease, occurring through theryanodine-sensitiveCaz+ characterize the requirementsand specificity for PIPz-inreleasechannel,displayedsaturation kinetics. The duced Ca2+release by flux studies performed in SR vesicles. rate ofCaz+releaseinducedby PIPz was approxi- We report here that PIP2can activatethe ryanodine-sensitive mately >50% slower than the rates induced by other SR Ca2+release channel in the presence of physiological M e and ATP and that low concentrations of PIP2 induce Ca2+ agents (e.g. caffeine, Caz+,ATP). PIP,, and not Ips, effectively elicited Caz+ release release from terminal cisternae. The stimulatory actions on from terminal cisternae.On the contrary,IP3, and not release from SR and on the channel appear to be unaffected PIPz,specifically mediated Caz+ release from dog brain by cytoplasmic [Ca"]. On the other hand, cytoplasmic IP, cerebellum microsomes, where IP3 receptors are activates the same channel only in low [Ca"] M). known tobefound.ThePIPz-inducedCaz+ release from muscle membranes was not dependent on medium MATERIALS AND METHODS [Ca"'] (from