NO MODULATES THE APICOLATERAL CYTOSKELETON OF ISOLATED HEPATOCYTES BYA PKC-DEPENDENT, CGMP-INDEPENDENT MECHANISM

Nitric oxide (NO) induces smooth muscle relaxation. We examined whethe r NO or its mediator of this action, guanosine 3',5'-cyclic monophosph ate (cGMP), similarly induces relaxation of the apicolateral cytoskele ton in hepatocytes. Apical (canalicular) contractions were observed in isolated rat hepatocyte couplets by videomicroscopy, tightjunction pe rmeability was determined in the couplets by paracellular penetration of Texas red-dextran, and cytosolic Ca2+ (Ca-i(2+)) was measured in is olated hepatocytes by fluorescence imaging. Unexpectedly, the NO donor sodium nitroprusside potentiated rather than inhibited apical contrac tion, in a cGMP-independent manner. This action of nitroprusside was b locked by hemoglobin or by inhibition of protein kinase C (PKC). Nitro prusside and 3-morpholinosydnonimine, another NO donor, each increased the permeability of hepatocyte tight junctions, a known effect of PKC in this cell type, and induced translocation of that kinase to the pl asma membrane, as determined by immunocytochemistry. Neither nitroprus side nor dibutyryl cGMP changed the amplitude or frequency of Ca-i(2+) signals in hepatocytes. Exogenous NO thus modulates the apicolateral cytoskeleton of hepatocytes via PKC activation rather than via cGMP or Ca-i(2+). These observations suggest a new role for NO: to activate P KC.