Inositol 1,4,5-trisphosphate–induced Calcium Release Is Necessary for Generating the Entire Light Response of Limulus Ventral Photoreceptors

The experiments reported here were designed to answer the question of whether inositol 1,4,5-trisphosphate (IP3)-induced calcium release is necessary for generating the entire light response of Limulus ventral photoreceptors. For this purpose the membrane-permeable IP3 receptor antagonist 2-aminoethoxydiphenyl borate (2APB) (Maruyama, T., T. Kanaji, S. Nakade, T. Kanno, and K. Mikoshiba. 1997. J. Biochem. (Tokyo). 122:498–505) was used. Previously, 2APB was found to inhibit the light activated current of Limulus ventral photoreceptors and reversibly inhibit both light and IP3 induced calcium release as well as the current activated by pressure injection of calcium into the light sensitive lobe of the photoreceptor (Wang, Y., M. Deshpande, and R. Payne. 2002. Cell Calcium. 32:209). In this study 2APB was found to inhibit the response to a flash of light at all light intensities and to inhibit the entire light response to a step of light, that is, both the initial transient and the steady-state components of the response to a step of light were inhibited. The light response in cells injected with the calcium buffer 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) was reversibly inhibited by 2APB, indicating that these light responses result from IP3-mediated calcium release giving rise to an increase in Cai. The light response obtained from cells after treatment with 100 μM cyclopiazonic acid (CPA), which acts to empty intracellular calcium stores, was reversibly inhibited by 2APB, indicating that the light response after CPA treatment results from IP3-mediated calcium release and a consequent rise in Cai. Together these findings imply that IP3-induced calcium release is necessary for generating the entire light response of Limulus ventral photoreceptors

Changes in the expression of voltage-gated K+ currents during development of human megakaryocytic cells

AbstractWe distinguished four distinct groups of megakaryocytic cells on the basis of their voltage-gated membrane currents. One group of 32 cells (15%), exhibited an inward rectifying current and had a diameter of 12±3.5 μm (mean±S.D.). A large group of 85 cells (39%) exhibited only a `leakage-like' current and had a diameter of 15.8±3.7 μm. The other two groups of cells exhibited voltage-gated outward currents. One group consisted of 43 `I-type' cells (19%), with a diameter of 22.3±3.4 μm, for which the maximal outward current occurred for a voltage step from −60 to either 0 or +20 mV. For the last group of 60 `M-type' cells (27%), which had a diameter of 26.7±2.9 μm, the maximal outward current occurred for a voltage step from −60 to +80 mV, the largest voltage step used. The currents recorded in this study, from megakaryocytes having `leakage-like' currents and `I-type' currents, were indistinguishable from the voltage-gated currents of the megakaryocytes from myelogenous leukemia patients, in which voltage-gated currents were suppressed (Kapural, L., O'Rourke, F., Feinstein, M.B. and Fein, A. (1995) Blood 86, 1043), suggesting that the megakaryocytes from the myelogenous leukemia patients are a dedifferentiated or less mature form of megakaryocyte

Rapid Increase in Plasma Membrane Chloride Permeability during Wound Resealing in Starfish Oocytes

Plasma membrane wound repair is an important but poorly understood process. We used femtosecond pulses from a Ti-Sapphire laser to make multiphoton excitation–induced disruptions of the plasma membrane while monitoring the membrane potential and resistance. We observed two types of wounds that depolarized the plasma membrane. At threshold light levels, the membrane potential and resistance returned to prewound values within seconds; these wounds were not easily observed by light microscopy and resealed in the absence of extracellular Ca2+. Higher light intensities create wounds that are easily visible by light microscopy and require extracellular Ca2+ to reseal. Within a few seconds the membrane resistance is ∼100-fold lower, while the membrane potential has depolarized from −80 to −30 mV and is now sensitive to the Cl− concentration but not to that of Na+, K+, or H+. We suggest that the chloride sensitivity of the membrane potential, after wound resealing, is due to the fusion of chloride-permeable intracellular membranes with the plasma membrane

Excitation of Limulus Photoreceptors by Hydrolysis-Resistant Analogs of cGMP and cAMP

cGMP was proposed to be the agent which directly opens the light-sensitive channel in Limulus ventral photoreceptors. However, the light-sensitive rhabdomeral-lobe (R-lobe) is not uniformly responsive to cGMP injection; that is, there are ‘hot spots’ of sensitivity. A potent phosphodiesterase which rapidly hydrolyses cGMP was suggested to explain the existence of these ‘hot spots’. To test this idea we injected ventral photoreceptors with hydrolysis-resistant cyclic nucleotide analogues. Whereas there can be a lack of a response to cGMP injection into the R-lobe, we find a reproducible depolarization upon R-lobe injection of hydrolysis-resistant cGMP analogues. Furthermore, the depolarization resulting from the injection of cGMP analogues does not require a rise in intracellular Ca2+, as it is not blocked by the Ca2+ buffer, BAPTA. Surprisingly, R-lobe injection of a hydrolysis-resistant cAMP analogue also depolarized ventral photoreceptors. Further work will be needed to resolve the role of cGMP in Limulus visual transduction

Age Is the Only Predictor of Poor Bowel Preparation in the Hospitalized Patient

We examine the impact of key variables on the likelihood of inpatient poor bowel preparation for colonoscopy. Records of inpatients that underwent colonoscopy at our institution between January 2010 and December 2011 were retrospectively extracted. Univariable and multivariable logistic regression models were fitted to assess the effect of clinical variables on the odds of poor preparation. Tested predictors included age; gender; use of narcotics; heavy medication burden; comorbidities; history of previous abdominal surgery; neurological disorder; product used for bowel preparation, whether or not the bowel regimen was given as split or standard dose; and time of endoscopy. Overall, 244 patients were assessed including 83 (34.0%, 95% CI: 28.1–39.9%) with poor bowel preparation. Cecal intubation was achieved in 81.1% of patients (95% CI: 76.2–86.0%). When stratified by quality of bowel preparation, cecal intubation was achieved in only 65.9% (95% CI: 60.0–71.9%) of patients with poor bowel preparation and 89.9% (95% CI: 86.1–93.7%) of patient with good bowel preparation. In multivariate logistic regression analysis, only advancing age was an independent predictor of poor bowel preparation (OR = 1.026, CI: 1.006 to 1.045, and p = 0.008). Age is the only independent predictor of poor bowel preparation amongst hospitalized patients

Antibiotic Treatment of the Tick Vector Amblyomma americanum Reduced Reproductive Fitness

BACKGROUND: The lone star tick Amblyomma americanum is a common pest and vector of infectious diseases for humans and other mammals in the southern and eastern United States. A Coxiella sp. bacterial endosymbiont was highly prevalent in both laboratory-reared and field-collected A. americanum. The Coxiella sp. was demonstrated in all stages of tick and in greatest densities in nymphs and adult females, while a Rickettsia sp. was less prevalent and in lower densities when present. METHODOLOGY/PRINCIPAL FINDINGS: We manipulated the numbers of both bacterial species in laboratory-reared A. americanum by injecting engorged nymphs or engorged, mated females with single doses of an antibiotic (rifampin or tetracycline) or buffer alone. Burdens of the bacteria after molting or after oviposition were estimated by quantitative polymerase chain reaction with primers and probes specific for each bacterial species or, as an internal standard, the host tick. Post-molt adult ticks that had been treated with rifampin or tetracycline had lower numbers of the Coxiella sp. and Rickettsia sp. and generally weighed less than ticks that received buffer alone. Similarly, after oviposition, females treated previously with either antibiotic had lower burdens of both bacterial species in comparison to controls. Treatment of engorged females with either antibiotic was associated with prolonged time to oviposition, lower proportions of ticks that hatched, lower proportions of viable larvae among total larvae, and lower numbers of viable larvae per tick. These fitness estimators were associated with reduced numbers of the Coxiella sp. but not the Rickettsia sp. CONCLUSION/SIGNIFICANCE: The findings indicate that the Coxiella sp. is a primary endosymbiont, perhaps provisioning the obligately hematophagous parasites with essential nutrients. The results also suggest that antibiotics could be incorporated into an integrated pest management plan for control of these and other tick vectors of disease