摘要:

Intravital microscopy was used to study the effect of endothelium-derived relaxing factor (EDRF) on microvascular adrenoceptor sensitivity in rat cremaster skeletal muscle.NG-Monomethyl l-arginine (L-NMMA, 1–300 μM), an inhibitor of EDRF formation, produced concentration-dependent constriction of arterioles and venules. When an intermediate amount of α1- versus α2-adrenoceptor tone was first produced with bath-added norepinephrine (NE) in the presence of rauwolscine or prazosin, L-NMMA caused constriction with greater potency and efficacy during α2than during α1tone. During localized α1or α2constriction along an arteriole by perivascular micropipette suffusion of NE in the presence of rauwolscine or prazosin, again, bath-added L-NMMA produced constriction with greater potency during α2than during α1constriction. Like L-NMMA, disruption of EDRF release by microembolization caused baseline arteriole constriction and selectively increased α2sensitivity 75-fold. Although these findings support the hypothesis that endothelial cells possess α2-adrenoceptors that promote EDRF release, a greater susceptibility of α2than α1constriction to EDRF inhibition could also account for the results. In support of this latter possibility, α2constriction was approximately 50-fold more susceptible than α1constriction to inhibition by the EDRF-like nitrodilator nitroprusside. The similarity in magnitude of this difference in sensitivity with the difference obtained in the embolization experiments does not support the hypothesis that microvascular endothelial cells in skeletal muscle possess EDRF-promoting α2-adrenoceptors. However, these data do suggest that endogenous EDRF release modulates basal arteriole and venule tone and that α2-adrenoceptor constriction is more sensitive thana, constriction to inhibition by EDRF.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

pHois an important determinant of vascular tone in cerebral blood vessels. We investigated the effects of changes in pH. on isolated smooth muscle cells from the basilar artery of the guinea pig. Single cells contracted rapidly in response to an elevation in pHo(constant CO2), and contraction was blocked by nifedipine, suggesting a role for dihydropyridine-sensitive Ca2+channels. In whole-cell patch-clamp experiments, changes in pHo(pHo5.7–8.1, pHi7.2 with 10 mM HEPES) strongly affected the amplitude of the peak Ca2+channel current (10 mM Ba2+, +15 mV, holding potential of −55 mV), with an apparent pK of 6.9. The current-voltage curves were minimally shifted, indicating no important effect of surface charge. To separate the slowly inactivating L-type Ca2+channel current from the more rapidly inactivating B-type current, the decaying portions of inward currents from cells studied with repetitive 1-second pulses (+15 mV, holding potential of −55 mV) were fit to a two-component model. Titration curves for the L-type and B-type currents indicated maximum increases by factors of 3.65 and 1.28 at alkaline pHoand gave apparent pK values of 7.71 and 6.47 (Hill coefficient unity). The time constant of inactivation for the B-type current at +15 mV was little affected by pHo, whereas that for the L-type current increased somewhat with increasing pHo. Additional experiments showed no significant effect of pHoon holding current or on voltage-activated outward currents (pCai7 with 11 mM EGTA). Our results provide additional evidence for participation of Ca2+channels in regulating basal tone in cerebral smooth muscle and indicate that pHoregulates current through slowly inactivating, dihydropyridine-sensitive L-type Ca2+channels.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The ATP dependence of the Na-Ca exchanger was investigated in isolated adult rat heart cells to evaluate the extent to which ATP depletion after a period of ischemia plus reperfusion in whole hearts could limit calcium uptake by Na-Ca exchange. A standard state for measurement of Na-Ca exchange activity that could be used with cells depleted of ATP to different degrees was defined. This was a state of zero sarcolemmal gradient for sodium, potassium, and pH and was achieved by incubation of the cells for 5 minutes with EDTA, EGTA, ouabain, and nigericin. Heterogeneity of cell ATP levels was minimized by using a protocol of total ATP depletion by incubation under conditions similar to ischemia, followed by reoxygenation to give partial restoration of ATP levels. No ATP was regenerated when cells were reoxygenated in the presence of rotenone, and such cells showed a very low rate of calcium uptake. Without rotenone, cells showed an almost complete restoration of Na-Ca exchange activity, in spite of a restoration of ATP levels to only one third of control values. Thus, the dependence of calcium uptake on ATP was highly nonlinear under these conditions. The calculatedKmfor ATP was no more than 10% of normal ATP levels. We conclude that ATP depletion after ischemia plus reperfusion is unlikely to limit the rate of calcium uptake through Na-Ca exchange in the whole heart if at least one quarter of the ATP is restored. In addition, we measured the apparent ATP dependence of calcium uptake by Na-Ca exchange in cells under conditions in which we previously had concluded that cell ATP distributions were very heterogeneous: when cells undergo contracture during incubation with oligomycin and without glucose. A linear relation between calcium uptake rate and ATP was observed at all ATP levels. This can be understood if cells in contracture that are incubated with oligomycin cannot take up calcium because of low ATP, whereas rod-shaped cells are able to retain a full uptake capability. This result further supports our conclusion that the ATP level declines catastrophically to near zero in these oligomycin-incubated cells just before contracture.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Low density lipoprotein (LDL) from patients with coronary atherosclerosis and diabetes mellitus as well as in vitro desialylated LDL, glycosylated LDL, and lipoprotein (a) caused a twofold to fourfold rise in cholesteryl ester in cultured human blood monocytes and intimal smooth muscle cells isolated from normal aorta. Native LDL from healthy subjects failed to induce intracellular lipid accumulation. We have demonstrated by laser correlative photometry and gel filtration chromatography that in vivo and in vitro modified lipoproteins form aggregates under cell culture conditions. The degree of modified lipoprotein aggregation directly correlated with the ability of these lipoproteins to elevate the cholesteryl ester content of cultured cells. Modified lipoprotein aggregates isolated by gel filtration induced a threefold to fivefold elevation in cellular cholesteryl ester content. Aggregates of125I-modified LDL were taken up and degraded fivefold to sevenfold more effectively as compared with nonaggregated lipoproteins. The uptake and degradation of125I-labeled aggregates were strongly inhibited by unlabeled aggregates, latex beads, and cytochalasin B but not by native or acetylated LDL. These data indicate that uptake of lipoprotein aggregates occurred by phagocytosis. Obtained results suggest that modified lipoprotein aggregation may be the key condition for lipid accumulation.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID