Direct measurement of energy metabolism in the isolated working rat heart

Fatty acids and carbohydrates are the two main energy substrates used by the heart. Studies involving the regulation of these pathways in the heart have historically been hampered by a number of important technical problems. One problem is the need to provide the heart with fatty acids, which, due to their insolubility, must be delivered to the heart either bound to albumin or contained within triacylglycerol-lipoproteins. Another problem is the need to perform experiments at relevant workloads, since the work performed by the heart is a key determinant of ATP production rates. The development of the isolated working heart preparation in the 1960s has been a very powerful tool to study energy metabolism. During this golden era of cardiac energy metabolism research, a number of techniques were developed that successfully overcame these two key problems. In this article, we describe refinements to this original preparation which has allowed for simultaneous measurement of both glycolysis and glucose oxidation, or simultaneous measurements of both lactate oxidation and fatty acid oxidation.