ABSTRACT: Various pharmacological agents designed to modulate plasma membrane ion channels seem to significantly affect intracellular Ca²? signaling when acting on their target receptor. Some agents could also cross-react (modulate channels or receptors beyond their putative target) with intracellular Ca²? transporters. This study investigated the potential of thirty putative modulators of either plasma membrane K?, Na?, or transient receptor potential (TRP) channels to cross-react with intracellular Ca²? release channels [i.e., ryanodine receptors (RyRs)] from skeletal muscle sarcoplasmic reticulum (SR). Screening for cross-reactivity of these various agents was performed by measuring the rate of spontaneous Ca²? leak or caffeine-induced Ca²? release from SR microsomes. Four of the agents displayed a strong cross-reactivity and were further evaluated with skeletal RyR (RyR1) reconstituted into planar bilayers. 6,12,19,20,25,26-Hexahydro-5,27:13,18:21,24-trietheno-11,7-metheno-7H-dibenzo [b,n][1,5,12,16]tetraazacyclotricosine-5, 13-diium dibromide (UCL 1684; K? channel antagonist) and lamotrigine (Na? channel antagonist) were found to significantly inhibit the RyR1-mediated caffeine-induced Ca²? release. TRP channel agonists anandamide and (-)menthol were found to inhibit and activate RyR1, respectively. High concentrations of nine other agents produced partial inhibition of RyR1-mediated Ca²? release from SR microsomes. Various pharmacological agents, especially TRP modulators, also inhibited a minor RyR1-independent component of the SR Ca²? leak. Overall, ?43% of the agents selected cross-reacted with RyR1-mediated and/or RyR1-independent Ca²? leak from intracellular stores. Thus, cross-reactivity should be considered when using these classes of pharmacological agents to determine the role of plasmalemmal channels in Ca²? homeostasis.
