Analysis of Conserved Glutamate and Aspartate Residues in Drosophila Rhodopsin 1 and Their Influence on Spectral Tuning.

The molecular mechanisms that regulate invertebrate visual pigment absorption are poorly understood. Studies of amphioxus Go-opsin have demonstrated that Glu-181 functions as the counterion in this pigment. This finding has led to the proposal that Glu-181 may function as the counterion in other invertebrate visual pigments as well. Here we describe a series of mutagenesis experiments to test this hypothesis and to also test whether other conserved acidic amino acids in Drosophila Rhodopsin 1 (Rh1) may serve as the counterion of this visual pigment. Of the 5 Glu and Asp residues replaced by Gln or Asn in our experiments, none of the mutant pigments shift the absorption of Rh1 by more than 6 nm. In combination with prior studies, these results suggest that the counterion in Drosophila Rh1 may not be located at Glu-181 as in amphioxus, or at Glu-113 as in bovine rhodopsin. Conversely, the extremely low steady state levels of the E194Q mutant pigment (bovine opsin site Glu-181), and the rhabdomere degeneration observed in flies expressing this mutant demonstrate that a negatively charged residue at this position is essential for normal rhodopsin function in vivo. This work also raises the possibility that another residue or physiologic anion may compensate for the missing counterion in the E194Q mutant.

The green-absorbing Drosophila Rh6 visual pigment contains a blue-shifting amino acid substitution that is conserved in vertebrates.

The molecular mechanisms that regulate invertebrate visual pigment absorption are poorly understood. Through sequence analysis and functional investigation of vertebrate visual pigments, numerous amino acid substitutions important for this adaptive process have been identified. Here we describe a serine/alanine (S/A) substitution in long wavelength-absorbing Drosophila visual pigments that occurs at a site corresponding to Ala-292 in bovine rhodopsin. This S/A substitution accounts for a 10-17-nm absorption shift in visual pigments of this class. Additionally, we demonstrate that substitution of a cysteine at the same site, as occurs in the blue-absorbing Rh5 pigment, accounts for a 4-nm shift. Substitutions at this site are the first spectrally significant amino acid changes to be identified for invertebrate pigments sensitive to visible light and are the first evidence of a conserved tuning mechanism in vertebrate and invertebrate pigments of this class.

Randomized trial of hematocrit 25% versus 35% during hypothermic cardiopulmonary bypass in infant heart surgery.

OBJECTIVES: We previously reported that postoperative hemodynamics and developmental outcomes were better among infants randomized to a higher hematocrit value during hypothermic cardiopulmonary bypass. However, worse outcomes were concentrated in patients with hematocrit values of 20% or below, and the benefits of hematocrit values higher than 25% were uncertain. METHODS: We compared perioperative hemodynamics and, at 1 year, developmental outcome and brain magnetic resonance imaging in a single-center, randomized trial of hemodilution to a hematocrit value of 25% versus 35% during hypothermic radiopulmonary bypass for reparative heart surgery in infants undergoing 2-ventricle repairs without aortic arch obstruction. RESULTS: Among 124 subjects, 56 were assigned to the lower-hematocrit strategy (24.8% +/- 3.1%, mean +/- SD) and 68 to the higher-hematocrit strategy (32.6% +/- 3.5%). Infants randomized to the 25% strategy, compared with the 35% strategy, had a more positive intraoperative fluid balance (P = .007) and lower regional cerebral oxygen saturation at 10 minutes after cooling (P = .04) and onset of low flow (P = .03). Infants with dextro-transposition of the great arteries in the 25% group had significantly longer hospital stay. Other postoperative outcomes, blood product usage, and adverse events were similar in the treatment groups. At age 1 year (n = 106), the treatment groups had similar scores on the Psychomotor and Mental Development Indexes of the Bayley Scales; both groups scored significantly worse than population norms. CONCLUSIONS: Hemodilution to hematocrit levels of 35% compared with those of 25% had no major benefits or risks overall among infants undergoing 2-ventricle repair. Developmental outcomes at age 1 year in both randomized groups were below those in the normative population.

The influence of hemodilution on outcome after hypothermic cardiopulmonary bypass: results of a randomized trial in infants.

BACKGROUND: We hypothesized that cognitive impairment and hemodynamic instability after infant cardiac surgery with cardiopulmonary bypass might be exacerbated by hemodilution. METHODS: In a single-center randomized trial with blinded assessment of outcomes, we compared use of 2 hemodilution protocols during hypothermic cardiopulmonary bypass with infant cardiac surgery. The primary perioperative end point was lowest cardiac index in the first 24 hours postoperatively, and primary end points at age 1 year were scores on the Psychomotor Development Index and Mental Developmental Index of the Bayley Scales. RESULTS: Among 147 subjects, 74 were assigned to the lower-hematocrit strategy (21.5% +/- 2.9%, mean +/- SD at onset of low-flow bypass) and 73 to the higher-hematocrit strategy (27.8% +/- 3.2%). In intent-to-treat analyses the lower-hematocrit group had lower nadirs of cardiac index (P =.02), higher serum lactate levels 60 minutes after cardiopulmonary bypass (P =.03), and a greater percentage increase in total body water on the first postoperative day (P =.006). Blood product use and adverse events were similar in the 2 groups. At age 1 year (113 children), the lower-hematocrit group had worse scores on the Psychomotor Development Index (81.9 +/- 15.7 vs 89.7 +/- 14.7, P =.008), as well as more Psychomotor Development Index scores at least 2 SDs below the population mean (16/56 [29%] vs 5/53 [9%], P =.01). The groups had similar Mental Developmental Index scores and findings on neurologic examination. Inferences using hematocrit as a continuous variable were similar to those based on intent-to-treat analyses. CONCLUSIONS: Hemodilution to a hematocrit level in wide use for cardiopulmonary bypass and thought to be safe is associated with adverse perioperative and developmental outcomes in infants.