Regulation of the calcium transient at the sarcolemma membrane

Schematic representation of the regulation of the calcium transient at the sarcolemma membrane. Calcium moves across the sarcolemma via the sodium-calcium exchanger (which uses the favorable electrochemical gradient for sodium to drive passive calcium transport) and the L-type calcium channel. Hormones and drugs that can affect this process include digoxin (which inhibits the Na-K-ATPase pump), epinephrine and isoproterenol (which bind the the beta receptor and activate adenylyl cyclase, leading to the formation of cyclic AMP), epinephrine and phenylephrine (which bind to the alpha receptor and activate phospholipase C), and milrinone and the methylxanthines (which are phosphodiesterase inhibitors, thereby slowing the metabolism of cyclic AMP and prolonging the beta adrenergic effect).