Pharmacologic differentiation between inositol-1,4,5-trisphosphate-induced Ca2+ release and Ca2+- or caffeine-induced Ca2+ release from intracellular membrane systems.
Various known Ca2+ channel blockers and intracellular Ca2+ antagonists have been tested for effects of inositol-1,4,5-trisphosphate (IP3)-induced Ca2+ release from isolated canine brain microsomes. In agreement with previous reports, heparin, p-chloromercuribenzoic acid, W-7, cinnarizine, flunarizine, certain local anesthetics, La3+, and Ca2+ inhibit the release of Ca2+ induced by addition of IP3. In addition, we report here pronounced inhibition of IP3-induced Ca2+ release by low levels of Cd2+, by relatively high concentrations of TMB-8, and by phytic acid. In contrast, a number of blockers of other Ca2+ channels (nifedipine, verapamil, dantrolene, dithiothreitol, and ruthenium red) have relatively little or no effect on IP3-induced Ca2+ release from brain microsomes. The relative ineffectiveness of substances that inhibit Ca2+- or caffeine-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum suggests that release of Ca2+ from caffeine- and IP3-sensitive neuronal Ca2+ stores is likely to be mediated by different channels. Further evidence that different channels are involved is presented by way of demonstration of the lack of Ca2+-induced Ca2+ release from these brain microsomes and the lack of effect on sarcoplasmic reticulum caffeine-induced Ca2+ release of certain inhibitors of IP3-induced Ca2+ release used here. Among IP3-induced Ca2+ release blockers, La3+ appeared to be exceptional in its ability to stimulate microsomal Ca2+ uptake sufficiently to attenuate release of Ca2+ induced by IP3. Most blockers of IP3-induced Ca2+ release appear not to function by way of inhibiting K+ counter-ion movements (valinomycin does not reverse the inhibition) but rather by way of direct interaction with the IP3 receptor or the Ca2+ channel that mediates the IP3-induced Ca2+ release. Inhibition of [3H]IP3 binding to the microsomes by phytic acid, heparin, pyrophosphate, p-chloromercuribenzoic acid, and Ca2+ could be demonstrated but not by the other substances tested.
Palade
P
P
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
Dettbarn
C
C
Alderson
B
B
Volpe
P
P
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002451:Cell Compartmentation / Q000187:drug effects; D004285:Dogs; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008861:Microsomes / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium