Abstract. C3bi receptors (CR3) on human polymorphonuclear leukocytes (PMN) bind ligand-coated particles and promote their ingestion. The binding activity of CR3 is not constitutive but is transiently enabled by phorbol esters (Wright, S. D., and B. D. Meyer, 1986, J. Immunol. 136:1759-1764. Our observations indicate that the capacity of CR3 to bind ligand is tightly correlated with the degree of ligand-independent aggregation of the receptor in the plane of the membrane. Fixed PMN were labeled with anti-CR3 monoclonal antibodies and streptavidin colloidal gold before viewing in the electron microscope either en face or in thin section. On unstimulated PMN, gold particles marking CR3 were dispersed randomly. Stimulation of PMN for 25 min with phorbol myristate acetate (PMA) dramatically enhances binding of C3bi-coated particles, and the CR3 on such stimulated cells was observed in clusters containing more than six gold particles. CR3 was not aggregated over coated pits. After 50 min in PMA, the binding activity of CR3 falls, and the distribution of CR3 was again observed to be disperse. If a hydrophilic phorbol ester was washed away after a 20-min stimulation, binding activity remains elevated for at least 50 min, and CR3 remained aggregated. Thus, clustering of CR3 was temporally correlated with its ability to bind ligand and initiate phagocytosis. Unlike CR3, Fc receptors and HLA did not exhibit changes in their aggregation state in response to PMA. Treating PMN with formyl-methionyl-leucyl-phenylalanine, which enhances expression of CR3 but not its function, did not lead to aggregation of CR3. These observations suggest that a clustered configuration is a precondition necessary for binding ligand and signaling phagocytosis.

Calcium signaling in fura-2 acetoxymethyl ester-loaded enteric glia was investigated in response to neuroligands; responses to AlP were studied in detail. Carbachol (1 mM), glutamate (100 jiM), norepinephrine (10 jiM), and substance P (1 pM) did not increase the intracellular calcium concentration ([Ca 24 ],) in cultured enteric glia. An increasing percentage of glia responded to serotonin (4%; 100 pM), bradykinin (11%; 10 1eM),

Acute gallbladder volvulus continues to remain a relatively uncommon process, manifesting itself usually during exploration for an acute surgical abdomen with a presumptive diagnosis of acute cholecystitis. The pathophysiology is that of mechanical organo-axial torsion along the gallbladder's longitudinal axis involving the cystic duct and cystic artery, and with a pre-requisite of local mesenteric redundancy. The demographic tendency is septua- and octo-genarians of the female sex, and its overall incidence is increasing, this being attributed to increasing life expectancy. We discuss two cases of elderly, fragile women presenting to the emergency department complaining of sudden onset right upper quadrant abdominal pain. Their subsequent evaluation suggested acute cholecystitis. Ultimately both were taken to the operating room where the correct diagnosis of gallbladder torsion was made. Pre-operative diagnosis continues to be a major challenge with only 4 cases reported in the literature diagnosed with pre-operative imaging; the remainder were found intra-operatively. Consequently, a delay in diagnosis can have devastating patient outcomes. Herein we propose a necessary high index of suspicion for gallbladder volvulus in the outlined patient demographic with symptoms and signs mimicking acute cholecystitis.

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In single fura 2-loaded myenteric neurons, caffeine caused concentration-dependent increases in intracellular Ca2+ concentration ([Ca2+]i) that were quantal, saturable, and reversible. Inhibition of caffeine-induced Ca2+ release was demonstrated by ryanodine (1 microM), dantrolene (10 microM), and procaine (5 mM). Caffeine and cyclopiazonic acid (30 microM) released overlapping Ca2+ stores, whereas the caffeine-releasable pool was a subset of Ca2+ released by the Ca2+ ionophore ionomycin (4 microM). Both mild depolarization (7.5 mM KCl) and a submaximal concentration of caffeine (1 mM) produced neuronal [Ca2+]i oscillations in one-third of cells examined, which could be abolished by ryanodine (1 microM) or removal of extracellular Ca2+. Release of caffeine-sensitive Ca2+ stores induced influx of extracellular Ca2+. Immunolocalization using confocal microscopy revealed ryanodine receptor-like staining within the cytosol of cultured myenteric neurons.