Calcium Antagonists and Calcium Agonists: Fundamental Criteria and Classification

Abstract

Excitation-contraction coupling is a Ca^{+ +}-dependent chain reaction that begins with superficial membrane depolarization and finishes with intracellular contractile tension development. The elucidation of the intermediate and the final links of this chain, i.e. of the interaction of Ca^{+ +} ions with intracellular organelles and with the protein constituents of the contractile system, has progressed tremendously during the past 3 decades. The name of Setsuro Ebashi [1] may be quoted here as being representative for many investigators who have decisively contributed to the striking achievements on this field of muscle research. Conversely, our own work delt with the initial events in excitation-contraction coupling, namely the transmembrane cation fluxes, particularly across the stimulated myocardial fibre membranes. The present article covers new developments that allow a reliable identification and classification of the drugs which inhibit or promote the Ca⁺⁺ currents specifically, i.e. without concomitant influences on Na⁺- or Mg^{+ +} -dependent sarcolemma membrane effects.