Carnitine and cardiac interstitium.

An important part of (acyl)carnitine may be stored in interstitial spaces and the external surface of adjacent cells. A high concentration of carnitine in the direct vicinity of cells may enhance the synthesis and export of long-chain acylcarnitine. Long-chain acylcoenzyme A, from which long-chain acyl carnitine is formed, cannot penetrate intact cell membranes. During hypoperfusion or ischemia, when long-chain acylcoenzyme A accumulates due to hampered fatty acid oxidation, there is an increased formation of long-chain acyl carnitine which diffuses into the interstitium and adjacent vascular endothelial cells. Due to its lipophilic nature and net positive charge (limitation of carboxyl-group dissociation in ischemic acidosis), long-chain acyl carnitine may decrease the affinity of Ca2+ to the cell surface and prevent Ca2+ overload of cells. The advantage of carnitine over many other cationic amphiphiles in the protection of areas of ischemia is that long-chain acyl carnitine is formed and stored only in ischemic areas.