Ca2+- and thromboxane-dependent distribution of MaxiK channels in cultured astrocytes: from microtubules to the plasma membrane.

Large-conductance, voltage- and Ca2+-activated K+ channels (MaxiK) are broadly expressed ion channels minimally assembled by four pore-forming alpha-subunits (MaxiKalpha) and typically observed as plasma membrane proteins in various cell types. In murine astrocyte primary cultures, we show that MaxiKalpha is predominantly confined to the microtubule network. Distinct microtubule distribution of MaxiKalpha was visualized by three independent labeling approaches: (1) MaxiKalpha-specific antibodies, (2) expressed EGFP-labeled MaxiKalpha, and (3) fluorophore-conjugated iberiotoxin, a specific MaxiK pore-blocker. This MaxiKalpha association with microtubules was further confirmed by in vitro His-tag pulldown, co-immunoprecipitation from brain lysates, and microtubule depolymerization experiments. Changes in intracellular Ca2+ elicited by general pharmacological agents, caffeine or thapsigargin, resulted in increased MaxiKalpha labeling at the plasma membrane. More notably, U46619, an analog of thromboxane A2 (TXA2), which triggers Ca2+-release pathways and whose levels increase during cerebral hemorrhage/trauma, also elicits a similar increase in MaxiKalpha surface labeling. Whole-cell patch clamp recordings of U46619-stimulated cells develop a approximately 3-fold increase in current amplitude indicating that TXA2 stimulation results in the recruitment of additional, functional MaxiK channels to the surface membrane. While microtubules are largely absent in mature astrocytes, immunohistochemistry results in brain slices show that cortical astrocytes in the newborn mouse (P1) exhibit a robust expression of microtubules that significantly colocalize with MaxiK. The results of this study provide the novel insight that suggests that Ca2+ released from intracellular stores may play a key role in regulating the traffic of intracellular, microtubule-associated MaxiK stores to the plasma membrane of developing murine astrocytes.

Cerebellar ataxia and Purkinje cell dysfunction caused by Ca2+-activated K+ channel deficiency.

Malfunctions of potassium channels are increasingly implicated as causes of neurological disorders. However, the functional roles of the large-conductance voltage- and Ca(2+)-activated K(+) channel (BK channel), a unique calcium, and voltage-activated potassium channel type have remained elusive. Here we report that mice lacking BK channels (BK(-/-)) show cerebellar dysfunction in the form of abnormal conditioned eye-blink reflex, abnormal locomotion and pronounced deficiency in motor coordination, which are likely consequences of cerebellar learning deficiency. At the cellular level, the BK(-/-) mice showed a dramatic reduction in spontaneous activity of the BK(-/-) cerebellar Purkinje neurons, which generate the sole output of the cerebellar cortex and, in addition, enhanced short-term depression at the only output synapses of the cerebellar cortex, in the deep cerebellar nuclei. The impairing cellular effects caused by the lack of postsynaptic BK channels were found to be due to depolarization-induced inactivation of the action potential mechanism. These results identify previously unknown roles of potassium channels in mammalian cerebellar function and motor control. In addition, they provide a previously undescribed animal model of cerebellar ataxia.

Acute effect of ursodeoxycholic acid on gallbladder volume in healthy subjects.

BACKGROUND: Although it has been shown that chronic administration of ursodeoxycholic acid increases gallbladder fasting and residual volume, it is unknown whether ursodeoxycholic acid exerts an acute effect on gallbladder volume. We therefore evaluated the effect of a single oral dose of ursodeoxycholic acid on gallbladder volume in healthy volunteers. METHODS: After the volunteers had fasted overnight, gallbladder volume was measured sonographically every 15 min for 5 h. Following a 1-h control period group I (n = 8) received ursodeoxycholic acid (1000 mg) orally with 100 ml of water, whereas group II (n = 8) received 100 ml of water (placebo) only. Gallbladder volumes were calculated, applying the sum-of-cylinders method. Serum levels of ursodeoxycholic acid were determined by gas chromatography at 1-h intervals. RESULTS: Gallbladder fasting volumes before ursodeoxycholic acid were similar in both groups (24.0 +/- 2.3 ml versus 25.4 +/- 3.3 ml; NS). After ingestion of ursodeoxycholic acid (group I) gallbladder volume increased rapidly, reaching 27.6 +/- 3.1 ml (p < 0.04) 1 h and 38.4 +/- 3.4 ml (p < 0.02) 4 h after ingestion of ursodeoxycholic acid. The individual gallbladder volumes after ingestion of ursodeoxycholic acid in group I increased to 146%-211% of pretreatment values. Ursodeoxycholic acid serum levels increased from 0.94 +/- 0.38 mumol/l to 10.51 +/- 1.36 mumol/l (p < 0.001) and correlated closely with gallbladder volumes (r = 0.80; p < 0.05). After ingestion of water only (group II) gallbladder volume decreased transiently from 15 min to 30 min after water intake and then remained at pretreatment values throughout the study period. CONCLUSION: Administration of a single oral dose of ursodeoxycholic acid causes a rapid increase in gallbladder volume, which reaches 163 +/- 10% of pretreatment volume at 4 h and is closely correlated with ursodeoxycholic acid serum levels.

Gallbladder emptying determines early gallstone clearance after shock-wave lithotripsy.

BACKGROUND/AIMS: Disappearance of gallbladder stones after shock-wave lithotripsy combined with bile acid therapy depends on mechanical evacuation and dissolution of fragments. Many patients with gallstones have impaired gallbladder emptying and may show delayed stone clearance after lithotripsy. METHODS: The effect of gallbladder emptying on gallstone clearance after lithotripsy was prospectively studied in 57 patients with one radiolucent gallbladder stone < or = 20 mm. Gallbladder emptying was assessed sonographically before and after 2 weeks of ursodeoxycholic acid (UDCA) treatment. RESULTS: UDCA increased gallbladder fasting and residual volume and decreased ejection rate but did not affect ejection fraction. Patients with an ejection fraction > 60% achieved complete gallstone clearance after lithotripsy in a higher percentage than patients with smaller ejection fractions (1 month, 31% vs. 7%, P = 0.022; 2 months, 55% vs. 18%, P = 0.003; 3 months, 66% vs. 29%, P = 0.005). Patients who became stone-free within 1 month showed larger ejection fractions than patients with retained fragments (67% +/- 4% vs. 56% +/- 3% before UDCA, P = 0.032; 65% +/- 4% vs. 53% +/- 3% with UDCA, P = 0.017). Further, ejection rate during UDCA therapy was larger in patients with complete gallstone disappearance within 1 month than in patients with delayed fragment clearance (1.57%/min +/- 0.36%/min vs. 0.76%/min +/- 0.09%/min; P = 0.002). CONCLUSIONS: Gallbladder emptying is a major determinant of early gallstone clearance after lithotripsy.

Recent time trends in uterine cancer.

Recent trends in corpus uterine cancer incidence rates were explored using 1979-86 data from the Surveillance and End Results Program (SEER); recent trends in hospitalizations for corpus uterine cancer were explored using 1979-86 data from National Hospital Discharge Surveys (NHDS); and recent trends in exogenous hormone use were delineated using data from the 1980, 1981, and 1985 National Ambulatory Medical Care Surveys (NAMCS). Uterine cancer incidence rates using SEER data have continued to decline since 1979. An acceleration in the decline since 1983-84 is suggested in all women and in women with intact uteri ages 45-64. Hospitalizations for uterine cancer have also declined since 1979, with a marked acceleration in the decline since 1983-84 for all women and for women ages 40-79 has increased 22 percent and use of unopposed exogenous estrogens in women of similar age has increased 7 percent, while use of exogenous progesterones have shown much more substantial increases of approximately 700 percent. Possible relationships between trends in exogenous hormone use and incidence rates of corpus uterine cancer are discussed.