NAD(P)H oscillations

NAD(P)H is well known as a major cellular source of reducing potential, important for many catabolic and biosynthetic reactions. However, NAD(P)H may also serve as a substrate for covalent protein modification or as a precursor of biologically active compounds, including cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinuclotide phosphate (NAADP+). cADPR and NAADP+ participate in cytosolic calcium release from intracellular stores, and the analysis of these functions has led to the emerging recognition of the importance of NAD(P) with respect to intracellular signal transduction (Cancela et al., 2000; Guse, 2000; Ziegler, 2000). We have recently reported that the cytoslic concentration of NAD(P)H in neutrophils and macrophages fluctuates in a periodic manner, and that not unlike Ca2+ oscillations, the amplitude and frequency of these oscillations appear to encode information, and are associated with signal transduction (Petty, 2000; Rosenspire et al., 2000; Kindzelskii et al., 1997). In particular, we have found that in spherical cells the NAD(P)H frequency is of the order of 3-4 minutes, but that upon polarization and adherence, a characteristic oscillation of about 20 seconds is superimposed upon the longer wave length oscillation. Both the amplitude and frequency of this shorter wavelength signal can be externally regulated by various cytokines, as well as the chemotactic signaling factor N-formyl-met-leu-phe (fMLP), and the tumor promoter and protein kinase C (PKC) activator, phorbol-12myristate-13-acetate (PMA) (Adachi et al., 1999; Kindzelskii et al., 1997). Thus, it appears that in neutrophils and macrophages, cytokine and other intracellular signaling cascades that are initiated by plasma membrane receptors involve FM and/or AM modulation of NAD(P)H oscillations (Adachi et al., 1999; Petty, 2000; Rosenspire et al., 2000). Surprisingly, we have also found that these (20 second) NAD(P)H oscillations are sensitive to electric fields, in that they will resonate with externally applied low power pulsed DC, (Kindzelskii and Petty, 2000) or AC fields (Rosenspire et al., 2000). Studies of the biological effects of extremely low frequency (ELF) electromagnetic fields is a field generally fraught with controversy and inconsistent results (Berg, 1999; McCann et al., 1998). Nevertheless, our findings on NAD(P)H resonance provide us with new insight, and potentially the key to understanding biological consequences of low power electromagnetic fields on cells. However, our previous studies have focused only on neutrophils and macrophages. We thought it important to demonstrate that ELF electric field resonance with NAD(P)H is a general phenomena, and one not restricted to cells of hematopoietic origin and, in particular, neutrophils and macrophages. Accordingly, this study focuses on the effect of pulsed DC fields on HT-1080 cells, a tumor cell line derived from a human fibrosarcoma of kidney origin (Rasheed et al., 1974). Although there are some differences, we have found that, as is the case for neutrophils and macrophages, NAD(P)H resonates with the electric fields, directly altering cellular physiology and function.