The developmental time, survival and reproduction of the cotton aphid, Aphis gossypii Glover (Hom., Aphididae), were evaluated on detached cotton leaves at five constant and two alternating temperatures (15, 20, 25, 30, 35, 25/30, and 30/35°C). The developmental periods of the immature stages ranged from 12.0 days at 15°C to 4.5 days at 30°C. A constant temperature of 35°C was lethal to the immature stages of A. gossypii. The lower developmental threshold for the cotton aphid was estimated at 6.2°C and it required 108.9 degree‐days for a first instar to become adult. The average longevity of adult females was reduced from 39.7 days at 15°C to 12.6 days at 30/35°C. The average reproduction rate per female was 51.5 at 25/30°C and 20.9 at 30/35°C. Mean generation time of the population ranged from 10.4 days at 30°C to 24.5 days at 15°C. The largest per capita growth rate (rm = 0.413) occurred at 30°C, the smallest at 15°C (rm = 0.177). It was evident that temperatures over 30°C prolonged development, increased the mortality of the immature stages, shortened adult longevity, and reduced fecundity. The optimal range of temperature for population growth of A. gossypii on cotton was 25/30–30°C.

The aim of this study was to determine the effects of a single exercise bout on luminal Cl(-) and Na(+) conductance in the respiratory epithelium of patients with cystic fibrosis (CF). In nine patients with CF and nine healthy control subjects, the transepithelial electrical potential difference (PD) of the nasal respiratory epithelium was recorded, first at rest and then during moderate-intensity exercise. Under both conditions, PD was first measured while superfusing the epithelium with isotonic saline. Then, the effects of amiloride and amiloride plus low chloride plus isoproterenol were determined. Exercise resulted in a significant lower PD compared with rest in patients with CF (-6.6 +/- 16.6 mV versus -33.6 +/- 10.0 mV, p < 0.0001) and control subjects (0.1 +/- 8.7 mV versus -7.1 +/- 5.1 mV, p < 0.01). The effects of amiloride on PD were reduced during exercise compared with rest in patients with CF (+15.8 +/- 9.5 mV versus +26.1 +/- 11.0 mV, p < 0.01) and control subjects (+5.8 +/- 4.8 mV versus +10.0 +/- 3.1 mV, p < 0.01). There was no effect of exercise on chloride conductance in patients with CF and control subjects. We conclude that moderate-intensity exercise partially blocks the amiloride-sensitive sodium conductance in the respiratory epithelium. The inhibition of luminal sodium conductance could increase water content of the mucus in the CF lung during exercise and may, in part, explain the beneficial effects of exercise in patients with CF.

Migration of transformed Madin-Darby canine kidney (MDCK-F) cells depends on the polarized activity of a Ca2+-sensitive K+ channel. We tested whether a gradient of intracellular Ca2+-concentration ([Ca2+]i) underlies the horizontal polarization of K+ channel activity. [Ca2+]i was measured with the fluorescent dye fura-2/AM. Spatial analysis of [Ca2+]i indicated that a horizontal gradient exists, with [Ca2+]i being higher in the cell body than in the lamellipodium. Resting and maximal levels during oscillations of [Ca2+]i in the cell body were found to be 135 +/- 34 and 405 +/- 59 nml/l, respectively, whereas they were 79 +/- 18 and 307 +/- 102 nmol/l in the lamellipodium. This gradient can partially explain the preferential activation of K+ channels in the plasma membrane of the cell body. We applied a local superfusion technique during migration experiments and measurements of [Ca2+]i to test whether its maintenance is due to an uneven distribution of Ca2+ influx into migrating MDCK-F cells. Locally superfusing the cell body of migrating MDCK-F cells with La3+ alone or together with charybdotoxin, a specific blocker of Ca2+-sensitive K+ channels, slowed migration to 47 +/- 10% and 9 +/- 5% of control, respectively. Local blockade of Ca2+ influx into the cell body and the lamellipodium with la3+ was followed by a decrease of [Ca2+]i at both cell poles. This points to Ca2+ influx occurring over the entire cell surface. This conclusion was confirmed by locally superfusing Mn2+ over the cell body and the lamellipodium. Fura-2 fluorescence was quenched in both areas, the decrease of fluorescence being two to three times faster in the cell body than in the lamellipodium. However, this difference is insufficient to account for the observed gradient of [Ca2+]i. We hypothesize that the polarized distribution of intracellular Ca2+ stores contributes significantly to the generation of a gradient of [Ca2+]i.

We isolated two cell clones from the wild-type Madin-Darby canine kidney cell line (MDCK) that resembles renal collecting duct epithelium. Morphology and karyotypes of the two cell clones were evaluated. The MDCK-C7 cell clone morphologically resembles principal cells (polygonal cell shape, flat), while the MDCK-C11 clone resembles intercalated cells (cuboidal cell shape, high). The diploid chromosome number of MDCK-C7 cells is 83.1 +/- 0.2 (n = 139); that for MDCK-C11 cells is 78.8 +/- 0.1 (n = 128). Culture of MDCK-C7 cells in alkaline medium (pH 7.7) induced irreversible phenotypical and genotypical alterations. Transformed MDCK-C7F cells are characterized by two abnormal (biarmed) chromosomes. In contrast, MDCK-C11 cells are not phenotypically altered by alkaline stress. In order to elucidate the role of intracellular pH (pHi) in the transformation process, we measured pHi under control conditions (pH 7.4), after 5 min exposure to alkaline stress ("acute experiment," pH 7.7) and after incubation of the cells in alkaline medium for two weeks ("chronic experiment," pH 7.7). Under control conditions, MDCK-C7 cells maintained pHi at 7.14 +/- 0.01 (n = 154) and MDCK-C11 cells at 7.01 +/- 0.01 (n = 147). Acute alkaline stress increased pHi of both cell types to similar steady-state values. Under chronic alkaline stress, MDCK-C7 cells were unable to maintain intracellular pH within normal limits exhibiting sustained alkalinization, whereas MDCK-C11 cells could successfully regulate pHi. We conclude that wild-type MDCK cells consist of two genetically distinct subpopulations with different morphology and function. Only the MDCK-C7 clone that resembles the principle cell type of renal collecting duct can be transformed by alkaline stress while the MDCK-C11 clone resists this treatment, due to efficient pHi control mechanisms.

The developmental time, survivorship and reproduction of Aphis gossypii Glover was evaluated on detached cucumber leaves at nine constant temperatures ranging from 15±1°C to 35±1°C in 2.5°C increments in the laboratory. Developmental periods of immature stages ranged from 10.8 days at 15°C to 4.1 days at 30°C and 32.5°C. Constant 35°C was lethal to immature stages of A. gossypii. The lower developmental threshold for the cotton aphid was estimated at 6.0°C and it required 92.6 degree-day development for a first instar to become adult. The average reproduction rate was 82.1 nymphs female À1 at 25°C and 2.3 nymphs female À1 at 32.5°C. The mean generation time of the population ranged from 6.8 days at 32.5°C to 22.8 days at 15°C. The highest per capita growth rate (r m =0.526) occurred at 25°C and the lowest at 15°C (r m =0.208) and 32.5°C (r m =0.132). It was evident that temperatures over 30°C prolonged development, increased mortality of immature stages, shortened adult longevity and reduced fecundity. The optimal range of temperature for population growth of A. gossypii on cucumber was very broad and ranged between 22.5°C and 30°C.