Striated muscle action potential assessment as an indicator of cellular energetic state

Action potentials of striated muscle are created through movement of ions through membrane ion channels. ATP-sensitive potassium (KATP) channels are the only known channels that are gated by the intracellular energetic level ([ATP]/[ADP] ratio). KATP channels are both effectors and indicators of cellular metabolism as part of a negative feedback system. Decreased intracellular energetic level alters the gating of KATP channels, which is reflected in alterations of the action potential morphology. These changes protect the cell from exhaustion or injury by altering energy-consuming processes that are driven by membrane potential. Assessing the effects of KATP channel activation on resting membrane potential and action potential morphology, and the relationship to cellular stress is important to the understanding of normal cellular function. To better understand how muscle cells adapt to energetic stress, the monophasic action potential (MAP) electrode and floating microelectrode were used to record action potentials in intact hearts and skeletal muscles, respectively. Intact organs provide a more physiological environment for the study of energetics and membrane electrical phenomena. Utilizing these techniques, a stress on the intracellular energetic state resulted in greater and faster shortening of the duration of cardiac action potentials, and hyperpolarization of the membrane of skeletal muscle in a KATP channel dependent manner. Motion artifacts are a limitation to studying transmembrane action potentials, but the MAP and floating microelectrode techniques uniquely allow for reading of action potential morphology uncoupled from motion artifacts. The use of the floating microelectrode in skeletal muscles is a novel approach that provides previously unavailable data on skeletal muscle membrane potentials in situ.