Cardiovascular Research vol:77 issue:2 pages:315-324
In the cardiac dyad, sarcolemmal L-type Ca2+ channels (LCCs) and sarcoplasmic reticulum (SR) Ca2+-release channels (RyR) are structurally in close proximity. This organization provides for an efficient functional coupling, tuning SR Ca2+ release for optimal contraction of the myocyte. Given that LCC are regulated by the prevailing [Ca2+], this structural organization is the setting for feedback mechanisms and crosstalk. A defective coupling of Ca2+ influx via LCC to activation of RyR has been implicated in reduced SR Ca2+ release in heart failure. Both functional changes in LCC properties and structural re-organization of LCC in T-tubules could be involved. LCC are regulated by cytosolic Ca2+, and crosstalk with SR Ca2+ handling occurs on a long-term basis, i.e. during steady-state changes in heart rate, on an intermediate-term basis, i.e. on a beat-to-beat basis during sudden rate changes, and on a very short- or immediate-term basis, i.e. during a single heartbeat. We review the properties and consequences of these different feedback mechanisms and the changes in heart failure and cardiac hypertrophy that have thus far been studied.