A rapid phosphate-induced depression of heart subsarcolemmal mitochondrial oxidative phosphorylation

Inorganic phosphate (Pi) was added to suspensions of interfibrillar (IFM) and subsarcolemmal (SLM) mitochondria. With 20 mM Pi, significant depression in SLM oxidative phosphorylation was seen after 60 seconds exposure whereas 120 seconds was required to depress IFM, although to a lesser degree. Oxidative phosphorylation rate of SLM was significantly depressed by 1 minute incubation with 2.5-20 mM Pi, whereas IFM were unaffected. Five minute incubation with similar Pi concentrations produced equal depression in both populations. We postulate that the rapid increase in intracellular Pi may contribute to contractile failure associated with early ischemia by depressing a critical pool of ATP synthesis represented by SLM.

Enhancement of clonidine-induced analgesia by lesions induced with spinal and intracerebroventricular administration of 5,7-dihydroxytryptamine

The role of serotonin (5-HT) in analgesia induced by clonidine was examined by determining the effect of intraspinal (i.s.) and intracerebroventricular (i.c.v.) injections of 5,7-dihydroxytryptamine (5,7-DHT) on analgesia produced by clonidine in the tail-flick and hot plate tests. Depletion of amines was verified by high performance liquid chromatography analysis. Intraspinal injections of 5,7-DHT potentiated the action of clonidine in both tests for analgesia and caused depletion of 5-HT in the spinal cord. Intracerebroventricularly injected 5,7-DHT also increased the action of clonidine and depleted 5-HT in brain as well as in the spinal cord. In the groups given intracerebroventricular injections, there appeared to be a biphasic increase in the action of the clonidine. Significant hyperalgesia from pretreatment with neurotoxin was observed only on a limited number of occasions. The present results indicate that 5-HT mechanisms in the CNS are important mediators of the analgesic action of clonidine. Interactions between clonidine and 5-HT systems at both spinal and supraspinal sites are considered.