Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC266
Preventive effect of mitochondrial substrates and calmodulin on L-type Ca2+ current in atrial cardiac myocytes of rabbit
H. Kim1, W. Kim1, J. Lee1, J. Kwon1, H. Baek1, C. Leem1
1. Department of Physiology, University of Ulsan College of Medicine, Seoul, Korea, Republic of.
L-type Ca2+ current (ICaL) is essential component to induce excitation-contraction coupling in cardiac myocytes. Therefore, ICaL is a major target of various signaling pathways. One of the difficulty to study on ICaL is run-down phenomena. In this study, we would like to see the role of mitochondria as a ATP factory. We enzymatically isolated single atrial myocytes of rabbit. All procedures were accorded with national legislation. It is well known that ICaL requires MgATP and calmodulin to maintain their function. However, even though 5 mM ATP is added in the pipette solution, ICaL became run-down and eventually disappeared. In this report, we tested the effect of mitochondrial substrates and calmodulin on ICaL maintenance. When we added pyruvate or malate, ICaL was maintained longer than that without the substrates. When we added malate and calmoduline together, ICaL was maintained much longer, even more than 1 hour. These results suggested that mitochondrial substrates were essential to support ICaL in sarcolemma and calmodulin was strong supportive effect on ICaL maintenance. Glucose was continuously present in the experimental conditions, however, only presence of glucose is not enough to support ICaL in whole cell patch clamp conditions. 5 mM ATP was continuously present but it could not prevent iCaL rundown which meaned that 5 mM ATP in pipette solution was not enough to maintain ICaL in sarcolemma. We tested NADH level in the presence of mitochondrial substrates such as pyruvate and malate and compared the maximum NADH level obtained in the presence of rotenone. Only presence of pyruvate could achieve 50% of the maximum NADH. In the presence of both malate and pyruvate, NADH level could reach more than 80% of the maximum NADH. These results suggested that the addition of the mitochondrial substrates was essential to maintain intracellular ATP level in whole cell patch conditions
Where applicable, experiments conform with Society ethical requirements