An increasing body of experimental evidence points to a crucial role for nucleoside diphosphate kinase (NDP kinase) in the development, differentiation and growth of cells. Alterations in NDP kinase expression or activity are correlated with malignancy and metastasis, and can be lethal in the early stages of development. In atrial cells, intracellular application of antibodies to NDP kinase impairs activation of potassium channels (K-Ach)) by agonist-bound muscarinic cholinergic receptors via the G protein Gk, implicating this enzyme in the regulation of transmembrane signalling in heart. The overall aim of this proposal is to understand the molecular mechanisms by which NDP kinase contributes to signal transduction pathways that underlie the physiological response of cardiac cells to neurotransmitters. The basic experimental system chosen is the isolated. adult atrial myocyte, which provides a unique opportunity to study NDP kinase function in vivo, at the cellular and molecular levels. The approach proposed involves patch clamp recording of receptormodulated ionic currents, combined with intracellular injection of purified enzyme and specific antibodies. With these tools, we hope to be able to dissect the contribution of NDP kinase to the early events resulting from stimulation of beta-adrenergic and muscarinic receptors, as reflected by changes in muscarinic K+ currents and calcium currents. Complementary biochemical and immunochemical techniques will also be applied in order to clarify the molecular aspects of these processes. Muscarinic and beta-adrenergic receptors affect profoundly myocardial excitability and contractility, and modulate other important physiological responses as well. Therefore, elucidation of the essential features of NDP kinase participation in signal transduction may be relevant to the understanding of the pathophysiology of chronic and acute processes where myocardial function is compromised.
