Conversion of xanthine dehydrogenase to oxidase in ischemic rat tissues.

In response to global ischemia, tissue xanthine dehydrogenase was converted to xanthine oxidase in all tissues with half-times of conversion at 37 degrees C of approximately 3.6, 6, 7, and 14 h for the liver, kidney, heart, and lung, respectively. The time course of enzyme conversion at 4 degrees C was greatly extended with half-conversion times of 6, 5, 5, and 6 d for the respective tissues. Increases in xanthine oxidase activity were accompanied by the appearance of a distinct new protein species with greater electrophoretic mobility. The oxidase from ischemic rat liver was purified 781-fold and found to migrate with a higher mobility on native gels than the purified native dehydrogenase. Sodium dodecyl sulfate profiles revealed the presence of a single major band of 137 kD for the native dehydrogenase, whereas the oxidase had been partially cleaved generating polypeptides of 127, 91, and 57 kD. Polypeptide patterns for the oxidase resemble those seen following limited in vitro proteolysis of the native dehydrogenase supporting a proteolytic mechanism for the conversion of xanthine dehydrogenase to oxidase in ischemic rat liver.

Unitary correlates of linguo-pharyngeal events in a dyskinetic rat model.

1. The hypoglossal nucleus unitary correlates of ketamine- and electrically induced tongue contractions and swallowing events were recorded and compared in stereotaxically mounted rats. 2. Very few of the units recorded could be identified as motoneurons by antidromic invasion through electrical stimulation of the hypoglossal nerve. 3. The sample consists of 109 units, 2/3 of which were located in the retrusor pool and 1/3 in the protrusor region. 4. Linguo-pharyngeal events were considered to be electrically induced if they followed consistently, and with a relatively fixed latency, a single electrical pulse delivered to the superior laryngeal nerve, and ketamine-induced if no such time-locked sequence existed or if they occurred in the absence of electrical stimulation. 5. No differences could be discovered between the two types of linguo-pharyngeal events whether they were compared at the polygraphic or the unitary level. 6. These findings suggest that pharmacologically (ketamine)-induced dyskinetic activity does not differ from comparable motor patterns induced by classical electrophysiological means.