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A permanent, ordered collection of 23,000 recombinant DNA plasmids containing Drosophila melanogaster DNA has been established. Simple and practical methods for storing and manipulating this collection were developed. In addition, an improved, simple and inexpensive method for making paper filter replicas of such an ordered collection and of a high density (10,000 colonies/petri dish) unordered collection was developed. These filter replicas are suitable for nucleic acid hybridization screens of recombinant DNA colinies and each filter replica can be used for many (greater than 5) successive screens. The kinetics of this hybridization reaction were examined and allow design of experiments that detect colony complementarity to a nucleic acid that is 0.5% of the hybridization probe.

The effect of atovarstatin on digoxin pharmacokinetics was assessed in 24 healthy volunteers in two studies. Subjects received 0.25 mg digoxin daily for 20 days, administered alone for the first 10 days and concomitantly with 10 mg or 80 mg atorvastatin for the last 10 days. Mean steady-state plasma digoxin concentrations were unchanged by administration of 10 mg atorvastatin. Mean steady-state plasma digoxin concentrations following administration of digoxin with 80 mg atorvastatin were slightly higher than concentrations following administration of digoxin alone, resulting in 20% and 15% higher Cmax and AUC(0-24) values, respectively. Since tmax and renal clearance were not significantly affected, the results are consistent with an increase in the extent of digoxin absorption in the presence of atorvastatin. Digoxin is known to undergo intestinal secretion mediated by P-glycoprotein. Since atorvastatin is a CYP3A4 substrate and many CYP3A4 substrates are also substrates for P-glycoprotein transport, the influence of atorvastatin and its metabolites on P-glycoprotein-mediated digoxin transport in monolayers of the human colon carcinoma (Caco-2) cell line was investigated. In this model system, atorvastatin exhibited efflux or secretion kinetics with a K(m) of 110 microM. Atorvastatin (100 microM) inhibited digoxin secretion (transport from the basolateral to apical aspect of the monolayer) by 58%, equivalent to the extent of inhibition observed with verapamil, a known inhibitor of P-glycoprotein transport. Thus, the increase in steady-state digoxin concentrations produced by 80 mg atorvastatin coadministration may result from inhibition of digoxin secretion into the intestinal lumen.

Scanning electron microscopic observations of the pulsed carbon dioxide laser effect on human enamel support microradiographic findings and indicate that this laser is significantly more efficient than the ruby laser within the limits of this investigation. Surface changes which were suggestive of fusion occurred between energy densities of 13 to 50 joules per square centimeter.There may be several potential applications of laser energy to dentistry. Initially, the use of the laser as a replacement for the dental drill was a popular idea,' but because of the high energy densities required this does not seem practical and has not been explored scientifically. Laser application to spectroscopic analysis of the chemical composition of substances related dentally has been attempted2?3 but still seems to be premature. The dental laboratory use of laser energy to solder and weld is in an early stage of development.4 In studying the effect of low laser energy densities, our interest has been ap-

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