The structural changes in bovine rod outer segments in the presence of ATP

Distribution of metabotropic P2Y receptors in the rat retina: a single-cell RT-PCR study

P2Y receptors are metabotropic G-protein linked purinergic receptors, which are especially widespread in the central nervous system. The purpose of the present study was to determine the distribution patterns of P2Y receptors in distinct retinal cell types in the adult retina. Retinal ganglion cells (RGC), bipolar cells (BPC) and Muller cells (MC) of adult pigmented rats were analyzed for their expression of P2Y-receptor subtypes P2Y1, P2Y2, P2Y4, and P2Y6 by single-cell reverse transcription polymerase chain reaction (SC-RT-PCR). SC-RT-PCR resulted in a positive amplification signal for all P2Y-receptor subtype mRNAs in all cell types examined. However, subtype distribution differed among the different cell types. The percentage of cells expressing a distinct P2Y subtype was: (a) for RGCs: 80% with P2Y1, 100% with P2Y2, 30% with P2Y4 and 50% with P2Y6, (b) for BPCs: 60% with P2Y1, 40% with P2Y2, 20% with P2Y4 and 80% with P2Y6, and (c) for MCs: 60% with P2Y1, 80% with P2Y2, 60% with P2Y4 and 100% with P2Y6. Our data show that different subtypes of P2Y receptors (P2Y1, P2Y2, P2Y4 and P2Y6) are expressed in various retinal cells and indicate that extracellular purines and pyrimidines act on RGCs, BPCs and MCs via different P2Y receptors.

Comparison of flash-induced light-scattering transients and proton efflux from auxinic-herbicide resistant and susceptible wild mustard protoplasts: a possible role for calcium in mediating auxinic herbicide resistance

Comparison of flash-induced light-scattering signals from protoplasts of auxinic herbicide-resistant ('R') and -susceptible ('S') wild mustard biotypes suggest that ATP-dependent activity manifested as a conformational change differs between the biotypes. The signal obtained from R protoplasts is unaffected by 50 microM picloram, an auxin analogue. In comparison, the signal amplitude from the S protoplasts decreases 40% in 20 microM picloram and is abolished in 50 microM picloram. Signal amplitude from the R protoplasts can be decreased by simultaneous incubation with 50 microM picloram and 50 microM verapamil, a calcium channel blocker. Incubation of the S protoplasts with the calcium ionophore A23187 in the presence of 0.5 mM calcium reduced the inhibitory effect of picloram. Absorbance spectrophotometry using acridine orange as a pH indicator suggests that picloram affects the proton flux in the S biotype only. Based on these results, we hypothesize that picloram affects the calcium and hydrogen dynamics in the S biotype. Because the scattering characteristics of S protoplasts incubated with picloram can be nearly reproduced in the R protoplasts by simultaneous incubation with picloram and verapamil, calcium may have a significant role in modulating auxinic herbicide resistance. To our knowledge, this is the first report to implicate such a role for calcium.

Study of retinal dystrophy in RCS rats: a comparison of Mg-ATP dependent light scattering activity and ERG b-wave

A comparative study using the techniques of ERG to measure the b-wave and light scattering relaxation spectrophotometry (LSRS) to determine the dynamic behavior Mg-ATP dependent processes in the rod photoreceptors of pigmented control and dystrophic RCS rats has been carried out. LSRS results, based exclusively on photoreceptor rod outer segment dynamics, suggest a progressive failure in the dark and light-induced Mg-ATP dependent processes as a function of age. The dark signal amplitude in the dystrophic rats decreases to about 50% of the control by 5 weeks post-natal; the light-induced signal has decreased by 30% in the same period. The ERG b-wave results indicate that the differences in the amplitude and the time required to attain the peak amplitude become increasingly pronounced between the control and dystrophic groups of rats again as a function of age. By 10 weeks of age, the intensity of light required to obtain a b-wave with a amplitude of 100 microM is 10(3) greater in the dystrophic RCS rats. Similarly, the time to achieve this peak increases in the dystrophs with age. These results indicate that the retinal dystrophy in the RCS rat affects the activity of the rod photoreceptor cells.