REDUCTION IN 2ND-MESSENGER LIGAND-BINDING SITES AFTER BRAIN ISCHEMIA - AUTORADIOGRAPHIC B(MAX) AND K(D) DETERMINATIONS USING DIGITAL IMAGE-ANALYSIS

Changes in forskolin (FK) and phorbol 12,13-dibutyrate (PDBu) binding were evaluated in relation to local cerebral blood flow (CBF) after 6- h unilateral carotid artery occlusion in the gerbil striatum employing a quantitative autoradiographic method, which permitted these three p arameters to be measured in the same brain. CBF was measured by the [C -14]iodoantipyrine method at the end of the experiment. [H-3]FK and [H -3]PDBu were utilized as specific ligands to assess the activity of ad enylate cyclase (AC) and protein kinase C (PKC), respectively. A satur ation study was undertaken to measure the K(d) (dissociation constant) and B(max) (maximal binding capacity) of each ligand by digital image processing of sequential autoradiograms employing pixel-by-pixel Scat chard analysis. The B(max) values of FK and PDBu were significantly de creased on the ischemic side, but the reduction in B(max) of FK was gr eater than that of PDBu. The K(d) of each ligand remained unchanged. T he FK binding underwent a progressive decline as CBF fell below 30 ml/ 100 g/min. The PDBu binding showed only a gradual decline in parallel with the CBF reduction. These findings suggest that a reduction in CBF below 30 ml/100 g/min for 6 h may induce a remarkable suppression of the AC system with less significant inhibition of the PKC system in th e striatum.