Characterization of a chimeric human dopamine D3/D2 receptor functionally coupled to adenylyl cyclase in Chinese hamster ovary cells.

Dopamine D3 receptor pharmacology differs from that of the dopamine D2 receptor despite a high degree of receptor sequence similarity. The greatest divergence of the primary sequences of D3 and D2 receptors occurs in the predicted third intracellular loops of the receptors, a region implicated in G protein binding and function. To determine whether this domain specifies the distinct ligand binding and signal transduction characteristics of the D3 receptor, we developed a chimeric receptor, replacing the third intracellular loop of the human D3 receptor with the third intracellular loop of the human D2 receptor. The pharmacology of the chimeric receptor expressed in Chinese hamster ovary cells was examined and compared with that of human dopamine D2 and D3 receptors expressed in the same cell line. The chimeric receptor retained characteristic human D3 receptor binding; the D2 third intracellular loop present in the chimeric receptor did not reduce high affinity agonist binding, characteristic of the D3 receptor, or make high affinity sites sensitive to GTP analogs. Unlike the native human D3 receptor, the chimeric receptor was negatively coupled to adenylyl cyclase through a pertussis toxin-sensitive pathway, apparently mediated by the D2 third intracellular loop. The ability of D3 ligand binding domains to produce a D2 functional response implies that the third intracellular loop of the D3 receptor is unable to mediate this D2 response in Chinese hamster ovary cells. The inhibition of adenylyl cyclase seen with the chimeric receptor is less than the inhibition produced by D2 receptor coupling, suggesting that additional sequences in the D2 receptor contribute to normal G protein coupling.

CI-1007, a dopamine partial agonist and potential antipsychotic agent. I. Neurochemical effects.

The receptor binding and biochemical effects of the putative dopamine (DA) partial agonist CI-1007 ([R(+)-1,2,3,6-tetrahydro-4-phenyl- 1-[(3-phenyl-3-cyclohexen-1-yl)methyl]pyridine] maleate) and potential antipsychotic were evaluated with a variety of biochemical methods. In receptor binding studies, CI-1007 bound to rat striatal DA receptors exhibiting a Ki of 3 nM as assessed by inhibition of [3H]N-propylnorapomorphine binding. CI-1007 also exhibited high affinity for cloned human D2L (Ki = 25.5 nM) and D3 (Ki = 16.6 nM) receptors with less affinity for D4.2 receptors (Ki = 90.9 nM). The affinity for serotonin-1A (5-HT-1A), alpha-2 adrenergic and 5-HT-2 receptors was moderate (submicromolar range) and slight or negligible for alpha-1, DA D1 and various other receptors. Unlike dopamine, the inhibition of [3H]spiperone binding was monophasic for CI-1007 and only slightly affected by the addition of Gpp-(NH)p. In vitro CI-1007 antagonized the forskolin-induced increases in cyclic AMP levels in GH4C1 cells expressing the human D2L receptor, having an intrinsic activity of 53% of that seen with the full agonist quinpirole. In vivo CI-1007 antagonized the gamma-butyrolactone (GBL)-induced accumulation of L-3,4-dihydroxyphenylalanine in striatum and mesolimbic regions of rat brain, causing a maximal 64% reversal in striatum, consistent with a partial agonist profile. In microdialysis studies it decreased DA overflow in both striatum and nucleus accumbens, indicating decreased release of DA. CI-1007 also reduced brain DA synthesis (DOPA accumulation), metabolism (DOPAC and HVA) and utilization (after tyrosine hydroxylase inhibition with alpha-methyl-p-tyrosine). CI-1007 did not affect striatal acetylcholine levels indicating lack of potent postsynaptic DA actions. CI-1007 seemed to be selective for DA neurons as it did not alter rat brain norepinephrine (NE) synthesis in the NE-enriched brainstem or NE utilization in the mesolimbic region. In addition, it did not affect in general 5-HT synthesis and metabolism in striatum and mesolimbic regions. These neurochemical results demonstrate that CI-1007 is a selective potent brain dopamine partial agonist with limited agonist activity at postsynaptic DA receptors.

Are medication error rates useful as comparative measures of organizational performance?

BACKGROUND: Although medication error rates seem a plausible indicator, it is not a foregone conclusion that error rates are good barometers of quality. METHODOLOGY: This article is based on a multisite, nationwide study of one contributor to medication errors: pharmacy dispensing errors. Using questionnaires, directors of pharmacy at 157 member hospitals of a national health care management firm reported their average daily medication dispensing loads and the number of dispensing errors per 100 patient days during one quarter. Stepwise discriminant analysis was used to seek characteristics of high versus low reported error rates, as well as characteristics that could distinguish hospitals that reported no errors from those that reported errors. DISCUSSION: Results show that currently measured error rates represent a process within an organization and can range from no or few errors to substantial errors, with the variation reflecting a variety of scenarios. Hospitals that do not measure error rates obviously report no errors. Inattention or a lack of clear methods to collect and define errors can also result in no reported errors or low error rates. In contrast, a hospital that standardizes and implements a measurement scheme may have high reported error rates. Progressive experimentation with systemwide error prevention and process improvement will result in varying error rates. Logically, if hospitals are punished for reporting high error rates, they will start reporting lower error rates regardless of the true rates. Finally, successful management practices will be reflected in low error rates. CONCLUSION: The focus on measuring medication error rates is important for improving quality within organizations because drug-related errors are an important cause of adverse events. However, the variances in error-reporting rates and the variables associated with those variances documented in this study raise serious questions about the usefulness of comparing error rates between hospitals based on voluntary reports. Interorganizational comparisons of rates are not likely to be meaningful and may be counterproductive.