ABSTRACT
Ceramide, which is an integral component of the sphingomyelin signaling pathway, can attenuate voltage-gated Ca(2+) channel (VGCC) activity in a number of cell types. The aim of the present study was to determine whether ceramide can also modulate VGCC activity, and as a consequence nicotinic receptor-dependent Ca(2+) signaling and catecholamine secretion, in rat adrenal chromaffin cells. Short-term C(6)-ceramide (CER) treatment dose-dependently inhibited nicotine (NIC)-induced peak intracellular Ca(2+) transients. Sphingomyelinase elicited similar responses, whereas the inactive ceramide analog C(2)-dihydroceramide had no effect on NIC-induced Ca(2+) transients. CER suppressed KCl- and NIC-induced Ca(2+) transients to a similar extent, suggesting that the voltage-gated Ca(2+) channel was a primary site of inhibition. In direct support of this concept, whole-cell patch-clamp analysis demonstrated that CER and sphingomyelinase significantly reduced peak Ca(2+) currents. Pretreatment with staurosporine significantly attenuated CER-dependent inhibition of both NIC-induced Ca(2+) transients and peak Ca(2+) current, suggesting that the effects of CER are mediated at least in part by protein kinase C. Consistent with suppressed Ca(2+) signaling, CER also significantly inhibited NIC-induced catecholamine secretion measured at the single-cell level by carbon fiber amperometry. This effect of CER was also significantly attenuated by pretreatment with staurosporine These data demonstrate that the sphingomyelin signaling pathway can modulate nicotinic receptor-dependent Ca(2+) signaling and catecholamine secretion in rat chromaffin cells.
Subject(s)
Adrenal Medulla/metabolism , Calcium Channels/metabolism , Calcium Signaling/physiology , Catecholamines/metabolism , Ceramides/metabolism , Chromaffin Cells/metabolism , Receptors, Nicotinic/metabolism , Sphingomyelins/metabolism , Adrenal Medulla/cytology , Animals , Calcium Channels/drug effects , Calcium Signaling/drug effects , Cells, Cultured/drug effects , Cells, Cultured/metabolism , Ceramides/pharmacology , Chromaffin Cells/drug effects , Dose-Response Relationship, Drug , Enzyme Inhibitors/pharmacology , Male , Membrane Potentials/drug effects , Membrane Potentials/physiology , Nicotine/pharmacology , Potassium Chloride/pharmacology , Protein Kinase C/antagonists & inhibitors , Protein Kinase C/metabolism , Rats , Rats, Sprague-Dawley , Receptors, Nicotinic/drug effects , Signal Transduction/drug effects , Signal Transduction/physiology , Sphingomyelin Phosphodiesterase/pharmacology , Staurosporine/pharmacologyABSTRACT
Seventeen methicillin-resistant Staphylococcus aureus (MRSA) with unique genotypes were examined to determine if resistance occurs more frequently with ciprofloxacin or levofloxacin. The mean single-step resistance rate to 4 x MIC of ciprofloxacin was 1.05 x 10(-5) (range <4.82 x 10[-11] to 5.06 x 10[-5]), and that to levofloxacin was 4.03 x 10(-6) (range <3.57 x 10[-13] to 4.10 x 10[-5]) (P < 0.05). When serially passaged, the mean MICs of ciprofloxacin and levofloxacin increased 3.0 +/- 1.5-fold and 1.8 +/- 1.4-fold, respectively (P < 0.05). Only four strains became resistant to levofloxacin, but eight became resistant to ciprofloxacin (P < 0.05). Ciprofloxacin selects resistant MRSA more frequently than levofloxacin.
Subject(s)
Ciprofloxacin/pharmacology , Drug Resistance, Microbial , Levofloxacin , Ofloxacin/pharmacology , Staphylococcus aureus/drug effects , Anti-Infective Agents/pharmacology , Methicillin Resistance , Microbial Sensitivity Tests , Staphylococcus aureus/physiologyABSTRACT
BACKGROUND: Streptococcus pneumoniae is one of the primary causes of illness and death among young children, and evidence suggests that the prevalence of antibiotic-resistant S pneumoniae is increasing. The purpose of this study was to investigate the prevalence of antibiotic-resistant S pneumoniae in a sample of children in day-care facilities in a region that includes both rural and urban communities. METHODS: Nasopharyngeal cultures were obtained from 104 children in eight day-care centers located in rural and urban central Kentucky in April and May, 1997. Thirty-five of the children produced isolates positive for S pneumoniae. Each isolate was tested for susceptibility to penicillin, trimethoprim-sulfamethoxazole, erythromycin, tetracycline, vancomycin, and cefotaxime. RESULTS: Of the children with S pneumoniae isolates, 54% had isolates that were resistant to penicillin and 40% that were resistant to trimethoprim-sulfamethoxazole. Twenty-one (60%) of the isolates had resistance to at least one of the six tested antimicrobials, with 15 (43%) having resistance to more than one of the antimicrobials. The mean age of children with isolates resistant to penicillin was significantly less (2.7 + 1.6) than those with penicillin-susceptible isolates (3.7 + 1.1, P = .02). There was no relation between resistance and rural or urban day-care location. CONCLUSIONS: A substantial proportion of S pneumoniae isolates in young children are resistant to antibiotics. Limiting the effect of S pneumoniae drug resistance may require a reexamination of outpatient treatment strategies for childhood respiratory tract infections.
