APStracts 2:0094G, 1995.

Nitric oxide modulates the apicolateral cytoskeleton of isolated rat hepatocyte couplets by a protein kinase c- dependent, ca2+- and cgmp-independent mechanism. Burgstahler, Angela D., and Michael H. Nathanson. Liver Study Unit and Center for Cell Imaging, Yale University School of Medicine, New Haven, CT

APStracts 2:0094G, 1995.

Nitric oxide induces smooth muscle relaxation. We examined whether nitric oxide or its mediator of this action, cGMP, similarly induces relaxation of the apicolateral cytoskeleton in hepatocytes. Apical (canalicular) contractions were observed in isolated rat hepatocyte couplets by videomicroscopy, tight junction permeability was determined in the couplets by paracellular penetration of Texas Red -dextran, and cytosolic Ca2+ was measured in isolated hepatocytes by fluorescence imaging. Unexpectedly, the nitric oxide donor sodium nitroprusside potentiated rather than inhibited apical contraction, and in a cGMP-independent manner. This action of nitroprusside was blocked by hemoglobin or by inhibition of protein kinase C. Nitroprusside and SIN-1, another nitric oxide donor, each increased the permeability of hepatocyte tight junctions, a known effect of protein kinase C in this cell type, and induced translocation of that kinase to the plasma membrane, as determined by immunocytochemistry. Neither nitroprusside nor dibutyryl cGMP changed the amplitude or frequency of cytosolic Ca2+ signals in hepatocytes. Exogenous nitric oxide thus modulates the apicolateral cytoskeleton of hepatocytes via protein kinase C activation rather than via cGMP or cytosolic Ca2+. These observations suggest a new role for nitric oxide: to activate protein kinase C.

Received 21 December 1994; accepted in final form 9 May 1995.
APS Manuscript Number G496-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.