Calcium Channel Blockers, Beta Blockers and the Maintenance of Calcium Homeostasis
A properly functioning myocardium is well equipped to maintain ionic homeostasis. Each myocyte is surrounded by a selectively permeable membrane into which are inserted the various ionic pumps, the ion-selective, voltage-activated and receptor operated channels, and the ion transporters, including the Na+-Ca2+ exchanger (Figure 1). In addition the cells contain an abundant capacity to synthesize energy-rich phosphates, provided that the supply of precursors, cofactors, substrate and oxygen does not become rate limiting. These energy-rich phosphates are needed not only as substrate for the myosin ATPase enzyme; they also provide the substrate for the various ionic pumps that are involved in maintaining intracellular ionic homeostasis. These pumps include the Na+-K+ ATPase, the plasmalemmal Ca2+ ATPase (Figure 1) and the Ca2+ ATPases of the mitochondria and the sarcoplasmic reticulum (S.R).
KeywordsIonic Homeostasis Ionic Pump Intercalate Disc Ischaemic Episode Slow Channel
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