A comparison of the effects of UTP and ATP on the Ca2 release channel of skeletal muscle sarcoplasmic reticulum

Heavy sarcoplasmic reticulum (SR) membrane fractions from rabbit and porcine skeletal muscle were incorporated into planar lipid bilayers and the activity of the Ca2+ release channels was recorded under voltage clamp, using Cs+ as the current carrier. The effects of the nucleotides adenosine triphosphate (ATP) and uridine triphosphate (UTP) on channel activity were studied at a holding potential of +30 mV. UTP (0.1-1.0 mM) had no effect per se on the conductance or the gating properties of the Ca2+ release channels. In contrast, ATP (>0.1 mM) increased Po, the open channel probability, and both to1 and to2, the open time constants, and decreased tc1 and tc2, the closed time constants. The Ca2+ channel conductance, however, was not affected by ATP. Ruthenium red (1-2 µM), a well-known inhibitor of the SR Ca2+ release channel, abolished the ATP-induced channel activation. These electrophysiological data provide support for our contention (G. Suarez-Kurtz et al (1993). Anais da Academia Brasileira de Ciências, 65: 330) taht the UTP-induced tension in mammalian "skinned" mmuscle fibers is not due to stimulated release of SR-stored Ca2+ via the release channel

Pharmacokinetics of oral ciprofloxacin in healthy, young Brazilian subjects

1. The pharmacokinetics of ciprofloxacin were determined in 8 healthy young volunteers (5 men and 3 women) after administration of single oral doses of 25omg. 2. The peak plasma concentration of ciprofloxacin (Cmax = 1.26 ñ 0.21 mg/l), the time to reach Cmax (Tmax = 1.99 ñ 0.26 h), the area under the time-plasma concentration curve (AUC = 5.52 ñ 0.84 mg h 1**-1), the terminal phase half-life (T1/2 = 3.05 ñ 0.56 h), the volume of distribution (Vd/F = 195.4 ñ 14.01) and total body clearance (CL/F = 46.3 ñ 2.61/h), both expressed as functions of the oral bioavailability (F) of ciprofloxacin were within the corresponding values reported in the literature for other healthy population groups. 3. Multiple dose administration (250 mg, po, twice daily for 4 days) did not result in accumulation of ciprofloxacin in plasma. No adverse side effects occurred during the study. 4. The pharmacokinetic data are discussed in relation to the minimum inhibitory concentration (MIC) of ciprofloxacin for a number of common pathogens isolated from human infections in Rio de Janeiro

Interaction of Bothrops venoms and antivenin on the release of creatine kinase from skeletal muscle

A polyvalent antivenin (5 micronl/ml) inhibited the increase in creatine kinase (CK) release from rat extensor digitorum longus muscles exposde to the venoms of B. jararacussu (20 microng/ml) or B. jararaca (150 microng/ml). The increase in plasma CK activity induced by intramuscular injection of B. jaracussu venon (2.5 microng/g) into mice was reduce by penetreatment with the antivenin and was abolished by preincubation of the venon with the ativenin. Changes in CK release from isolated muscles or in plasma CK activity provide simple, quantitative methods for evaluating the effectiveness of antivenin against the myotoxicity of Bothrops venoms