Mode of action of ergonovine on isolated porcine coronary artery: the role of Ca2+

Coronary vasoconstrictor responses to ergonovine were examined in helical coronary arterial strips of young swine. Both ergonovine and serotonin (5-hydroxytryptamine) produced dose-dependent contractions of the strips. The distal region (less than 1.00 mm outer diameter) of the circumflex coronary artery was most sensitive to the responses of serotonin and ergonovine. Methysergide and nifedipine significantly depressed the contractions induced by ergonovine and serotonin. Atropine, propranolol, and the alpha 1 blocker, prazosin, did not antagonize ergonovine-induced contractions. The ergonovine response may depend entirely upon extracellular Ca2+ while the effect of serotonin may be mediated in part through the mobilization of intracellular Ca2+ stores. Increases in 45Ca2+ cellular contents occurred after ergonovine or serotonin and these increases were blocked by methysergide or nifedipine at concentrations which blocked mechanical responses to the agonist. It is concluded that the contractions of the porcine coronary artery produced by ergonovine and serotonin are as follows: (i) regionally sensitive; (ii) blocked by Ca2+ antagonists and therefore may utilize Ca2+ channels similar to those described in other excitable tissues; (iii) blocked by methysergide. These studies indicate that the major mechanism of ergonovine's action in the porcine coronary artery is through the activation of serotonin receptors on coronary arteries which are, in turn, linked to Ca2+ channels. However, this mechanism of action may be different in an intact animal.     

Impetigo—Bacteriologic Features and Renal Involvement

One hundred children with impetigo were studied with particular emphasis upon the organism causing the infection and associated renal complications. In 50 per cent of cases, Group A beta-hemolytic streptococcus grew on cultures of material from the lesions, and evidence of recent infection with this organism as shown by an elevation of antistreptolysin O titer was present in an additional 17 per cent of cases.Acute glomerulonephritis developed in three of the 66 children with bacteriologic or serologic evidence of streptococcal infection. Four other children in this group and nine children with staphylococcal impetigo had unexplained microscopic hematuria.All children with nephritis already had evidence of the disease when first seen. In most of those with unexplained hematuria, this condition was detected at the first visit. Hematuria developed in others while they were receiving systemic antibiotics. The significance of isolated microscopic hematuria is uncertain, but is seen often in association with cutaneous infection with both staphylococcus and streptococcus. Microscopic hematuria as defined is apparently not prevented by antibiotic therapy.If acute glomerulonephritis that follows streptococcal cutaneous infection is to be prevented, streptococcal impetigo will have to be treated promptly after onset.     

The feeding ecology of three species of Caribbean angelfishes (family Pomacanthidae)

Synopsis The foraging behavior and associated morphology of the feeding apparatus of three sympatric species of angelfishes, Holacanthus tricolor, Pomacanthus arcuatus and Pomacanthus paru were studied at St. Croix, U.S. Virgin Islands. All three had overlapping diets, consisting of algae and numerous species of sponges. The two Pomacanthus species also fed on gorgonians. The morphology of the dentition, jaws and gill rakers was similar in all three species. Male Holacanthus tricolor defended territories overlapping the foraging areas of two to four females. Within the male's territory, females defended smaller territories against other females of the same size, but tolerated smaller females. In contrast, both Pomacanthus spp. formed pairs which defended intraspecific feeding territories.     

THE IMPACT OF A FLOWER-COLOR POLYMORPHISM ON MATING PATTERNS IN EXPERIMENTAL POPULATIONS OF WILD RADISH (RAPHANUS RAPHANISTRUM L.)

We conducted field experiments to determine how a naturally occurring petal-color polymorphism influences mating patterns in wild radish (Raphanus raphanistrum). The polymorphism is controlled at a single genetic locus, with white petal color being completely dominant to yellow. In experimental populations with equal numbers of yellow- and white-flowered homozygous individuals, insect visitors strongly discriminated against white flowers. Pieris rapae, the most frequent pollinator, was almost 50% more likely to visit yellow than white flowers. Maternal fecundity did not differ between the morphs and was not significantly influenced by a plant's compatibility with potential donors, suggesting that seed production was not limited by receipt of compatible pollen. In contrast, the yellow-flowered morph sired approximately 75% of all seeds produced during the study. This paternity proportion was consistently greater than that expected on the basis of postpollination compatibility measures and was indistinguishable from that expected on the basis of pollinator-visitation frequency. We conclude that the male-fitness advantage of the yellow morph resulted from enhanced pollen export due to the greater attractiveness of its flowers to insect pollinators. With color morphs evenly distributed in experimental arrays, insects did not move assortatively on the basis of petal color, and we found no evidence for assortative pollen flow due to the floral polymorphism. Once postpollination compatibility relationships within populations were taken into account, paternal success of yellow donors did not differ between yellow- and white-flowered maternal plants.     

Rapid release of bound glucose-6-phosphate dehydrogenase by growth factors. Correlation with increased enzymatic activity

Epidermal growth factor (EGF), a mitogen for renal proximal tubule cells, activated the hexose monophosphate (HMP) shunt in renal proximal tubule cells (Stanton, R. C., and Seifter, J. L. (1988) Am. J. Physiol. 254, C267-C271). We therefore evaluated the effect of EGF on the HMP shunt enzymes glucose 6-phosphate dehydrogenase (G6PD, the rate-limiting enzyme) and 6-phosphogluconate dehydrogenase. Rat renal cortical cells (RCC) were incubated with either EGF or platelet-derived growth factor (PDGF) and then assayed for G6PD and 6-phosphogluconate dehydrogenase activities. EGF and PDGF increased G6PD activity by 25 and 27% respectively. Although phorbol myristate acetate (PMA), ionomycin, PMA + ionomycin, and 8-bromo-cyclic AMP had no significant effect on the activity, a 5-min preincubation with PMA potentiated the activation of G6PD by PDGF. Growth factor activation of G6PD was also seen in a fibroblast and epithelial cell line. None of the agents affected 6-phosphogluconate dehydrogenase activity in the RCC or in the cell lines. Further exploration into a possible mechanism for G6PD activation revealed that growth factors caused release of G6PD from a structural element within the cell. Streptolysin O permeabilization of RCC did not cause significant release of G6PD. However, within 1 min of addition of EGF or PDGF to permeabilized cells, G6PD was released into the cell supernatant. The nonhydrolyzable analog of GTP, guanosine 5'-O-(thiotriphosphate), caused a similar release of G6PD. Preincubation with pertussis toxin or guanyl-5'-yl thiophosphate inhibited the PDGF but not the EGF effect. Although the data do not establish a definitive proof linking G6PD release and G6PD activation, these results suggest that they are related. Thus, growth factor stimulation of the HMP shunt likely occurs by a novel mechanism associated with release of bound G6PD.     

A macrophage Fc receptor for IgG is also a receptor for oxidized low density lipoprotein.

The internalization of oxidized low density lipoprotein (OxLDL) by macrophages is hypothesized to contribute to foam cell formation and eventually to atherosclerotic lesion formation. OxLDL is a ligand for the acetylated low density lipoprotein (AcLDL) receptor, however, our data show that this receptor accounts for less than half of OxLDL uptake by mouse macrophages, suggesting additional receptors for OxLDL. We have developed a novel expression cloning strategy in order to isolate clones encoding OxLDL receptors. In addition to the AcLDL receptor, we isolated a molecular clone for a structurally unrelated receptor capable of mediating the high affinity uptake of OxLDL following transfection into cells. This receptor has been identified as the mouse Fc gamma RII-B2, a member of a family of receptors known to mediate immune complex uptake through recognition of the Fc region of IgG. The uptake of OxLDL by cells transfected with the Fc gamma RII-B2 clone is not blocked by AcLDL but is blocked by the anti-Fc gamma RII monoclonal antibody, 2.4G2.