P-Glycoprotein, the plasma membrane protein responsible for the multidrug resistance of some tumour cells, is an active transporter of a number of structurally unrelated hydrophobic drugs. We have characterized the modulation of its ATPase activity by a multidrug-resistance-related cytotoxic drug, vinblastine, and different multidrug-resistance-reversing agents, verapamil and the dihydropyridines nicardipine, nimodipine, nitrendipine, nifedipine and azidopine. P-Glycoprotein ATPase activity was measured by using native membrane vesicles containing large amounts of P-glycoprotein, prepared from the highly multidrug-resistant lung fibroblasts DC-3F/ADX. P-Glycoprotein ATPase is activated by verapamil and by nicardipine but not by vinblastine. Among the five dihydropyridines tested, the higher the hydrophobicity, the higher was the activation factor with respect to the basal activity and the lower was the half-maximal activating concentration. The vinblastine-specific binding on P-glycoprotein is reported by the inhibitions of the verapamil- and the nicardipine-stimulated ATPase. These inhibitions are purely competitive, which means that the bindings of vinblastine and verapamil, or vinblastine and nicardipine, on P-glycoprotein are mutually exclusive. In contrast, verapamil and nicardipine display mutually non-competitive interactions. This demonstrates the existence of two distinct specific sites for these two P-glycoprotein modulators on which they can bind simultaneously and separately to the vinblastine site. The nicardipine-stimulated ATPase activity in the presence of the other dihydropyridines shows mixed-type inhibitions. These dihydropyridines have thus different binding sites that interact mutually to decrease their respective, separately determined affinities. This could be due to steric constraints between sites close to each other. This is supported by the observation that vinblastine binding is not mutually exclusive with nifedipine or nitrendipine binding, whereas it is mutually exclusive with nicardipine. Moreover, verapamil binding also interacts with the five dihydropyridines by mixed inhibitions, with different destabilization factors. On the whole our enzymic data show that P-glycoprotein has distinct but interacting binding sites for various modulators of its ATPase function.

The results are presented of a study of the accuracy one may achieve at HERA in measuring the strong coupling constant $\alpha_s$ and the gluon distribution $xg(x,Q^{2})$ using future data of the structure function $F_{2}(x,Q^{2})$ which are estimated to be accurate at the few % level over the full accessible kinematic region down to $x \simeq 10^{-5}$ and up to $Q^{2} \simeq 50000 GeV^{2}$. The analysis includes simulated proton and deuteron data, and the effect of combining HERA data with fixed target data is discussed.

Inelastic channels in ${\ensuremath{\pi}}^{\ensuremath{-}}p$ interactions at 205 GeV/c are studied as a function of charged-particle multiplicity ${n}_{\mathrm{ch}}$. Experimental tests are made which are sensitive to the charge-dependent behavior of the particles, particularly at high and low rapidities. A set of new variables useful for the study of these processes is introduced. Effects which may be attributed to leading particles or leading jets are present to some extent for all ${n}_{\mathrm{ch}}$. Among the results presented, it is shown that at this energy there is no "central region" which is completely free of effects which are correlated with the charges of the incident particles. Qualitative interpretation of the results in terms of cluster-model ideas is presented; a specific simple model is calculated and compared with the data.

Neutral-strange-particle production has been studied in a 46000-picture exposure in the Fermilab 15-ft bubble chamber. Cross sections for inclusive production of ${K}_{s}^{0}$, $\ensuremath{\Lambda}$, and $\overline{\ensuremath{\Lambda}}$ are given and compared with data at lower energies. The ${K}_{s}^{0}$'s are produced principally in the central region of rapidity with a cross section which increases with energy. The $\ensuremath{\Lambda}$'s are produced principally by proton fragmentation, whereas the $\overline{\ensuremath{\Lambda}}$'s are centrally produced. Correlations of ${K}_{s}^{0}{\ensuremath{\pi}}^{+}$ and ${K}_{s}^{0}{K}_{s}^{0}$ are shown to be different from those for ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$.

A study of 205-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}p$ interactions has been made with a 48 800-picture exposure in the bare Fermilab 30-inch hydrogen bubble chamber. The average number of charged particles produced per inelastic interaction is 7.99\ifmmode\pm\else\textpm\fi{}0.06. The elastic cross section is 3.18\ifmmode\pm\else\textpm\fi{}0.13 mb and the total cross section is 24.19\ifmmode\pm\else\textpm\fi{}0.44 mb. The inclusive cross sections for neutral-particle production are: $\ensuremath{\sigma}(\ensuremath{\gamma})=171.3\ifmmode\pm\else\textpm\fi{}15.3$ mb, $\ensuremath{\sigma}({K}_{S}^{0})=3.64\ifmmode\pm\else\textpm\fi{}0.61$ mb ($x<0.3$), $\ensuremath{\sigma}(\ensuremath{\Lambda})=1.71\ifmmode\pm\else\textpm\fi{}0.34$ mb ($x<0.3$), and $\ensuremath{\sigma}(\overline{\ensuremath{\Lambda}})=0.59\ifmmode\pm\else\textpm\fi{}0.23$ mb ($x<0.1$). The average number of ${\ensuremath{\pi}}^{0}'\mathrm{s}$ produced per inelastic collision is consistent with a linear rise with the number of charged particles, and about equal to the number of produced ${\ensuremath{\pi}}^{\ensuremath{-}}$ or ${\ensuremath{\pi}}^{+}$. The average number of ${K}^{0}'\mathrm{s}$, $\ensuremath{\Lambda}'\mathrm{s}$, and $\overline{\ensuremath{\Lambda}}'\mathrm{s}$ is consistent with very little dependence on the number of charged particles. General characteristics of neutral-particle production are presented and compared with other experiments. For each topology the produced neutral energy is $\ensuremath{\sim}\frac{1}{3}$ of the incident energy.

The inclusive ϱ° production cross section has been measured in the reaction π−p → π+π−X at 205 GeV/c. We find σ(ϱ°) = 13.5 ± 3.4 mb, with most of the production occuring in the central region. Assuming σ(ϱ+) ≈ σ(ϱ−) ≈ σ(ϱ°), it is concluded that approximately one-third of the pions at this energy come from ϱ-decay.

Pion diffraction dissociation into masses up to approximately 6 GeV is observed in the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}p+X$ at 205 GeV/c. The pion single-diffraction cross section for mass squared \ensuremath{\le} 32 Ge${\mathrm{V}}^{2}$ is 1.9 \ifmmode\pm\else\textpm\fi{} 0.2 mb.

Author(s): Winkelman, F.C.; Bingham, H.H.; Chew, D.M.; Daugsras, B.Y.; Fretter, W.B.; Goldhaber, G.; Graves, W.R.; Johnson, A.D.; Kadyk, J.A.; Stutte, L.; Trilling, G.H.; Yost, G.P.; Bogert, D.; Hanft, R.; Huson, F.R.; Kahn, S.; Ljung, D.; Pascaud, C.; Pruss, S.; Smart, W.M.

A number of experiments at beam momenta below {approx} 25 GeV/c have yielded results on {pi}{sup -}{pi}{sup +} and {pi}{sup -}{pi}{sup -} scattering cross sections, obtained by modified Chew-Low extrapolation techniques applied to the reactions {pi}{sup -}p {yields} {Delta}{sup 0}{pi}{sup +}{sup -}. They have applied these same techniques to a small sample (169 events) of the reaction {pi}{sup -}p {yields} p{pi}{sup +}{pi}{sup -}{pi}{sup -} obtained from a 48,000-photo exposure of the NAL 30-inch hydrogen bubble chamber to a 205 GeV {pi}{sup -} beam. The statistics are insufficient to test the validity of the analysis at these high energies but they find {pi}{sup -}{pi}{sup +} and {pi}{sup -}{pi}{sup -} elastic scattering cross sections in the M{sub {pi}{sup {+-}}{pi}{sup -}} {approx} 3 GeV. Results will be presented of an attempt to obtain inelastic and total {pi}{pi} scattering cross-section estimates under similar assumptions.

Pion and proton diffraction dissociation are observed in π−p interactions at 205 GeV/c. The 2‐ and 4‐prong final states show evidence for N* and A1 production. Pion diffraction into masses up to ∼ 6 GeV is observed in the inclusive reaction π−p ⇒ p + X.

Results are reported based on a study of 3114 ${\ensuremath{\pi}}^{\ensuremath{-}}p$ events at 205 GeV/c in the National Accelerator Laboratory 30-in. bubble chamber. The measured ${\ensuremath{\pi}}^{\ensuremath{-}}p$ total and elastic cross sections are 24.0 \ifmmode\pm\else\textpm\fi{} 0.5 and 3.0 \ifmmode\pm\else\textpm\fi{} 0.3 mb, respectively. The elastic differential cross section has a slope of 9.0 \ifmmode\pm\else\textpm\fi{} 0.7 ${\mathrm{GeV}}^{\ensuremath{-}2}$ for $0.03\ensuremath{\le}\ensuremath{-}t\ensuremath{\le}0.6$ ${\mathrm{GeV}}^{2}$. The average charged-particle multiplicity for the inelastic events is 8.02 \ifmmode\pm\else\textpm\fi{} 0.12.