Alteration by phosphatidyl serine of tension responses and 45Ca distribution in aortic smooth muscle

The effects of phosphatidyl serine (PS) on 45Ca distribution, 45Ca movements and contractions were examined in rabbit aortic smooth muscle. Contractile responses to submaximal concentrations of norepinephrine and histamine were potentiated by prior exposure to PS, but equivalent responses to potassium were unaffected. Addition of PS to the incubation solution decreased 45Ca uptake; exposure of aortic strips to PS during washout of either 45Ca or promethium (147Pm) resulted in maintained increases in efflux. These PS-induced alterations in net loss of 45Ca or 147Pm can be attributed to a decreased membrane reuptake and/or rebinding. However, the presence of PS during the washout significantly reduced the increases in 45Ca efflux rate elicited with either 0.05 mM concentrations of Ca++ or ethylenediamine tetraacetic acid. Thus, in rabbit aortic smooth muscle, exogenous PS can alter the availability and/or exchangeability of a membrane-bound Ca++ fraction. By specifically increasing the affinity for Ca++ at relevant membrane sites or stores. PS may enhance the ability of vascular smooth muscle to respond to stimulatory agents that mobilize Ca++ from these sites and, in this manner, potentiate contractile responses.     

Carbon dioxide field flooding minimizes residual intracardiac air after open heart operations

Transesophageal echocardiographic studies were used to monitor the presence of air bubbles in the heart after open heart operations. After cardiac valvular procedures all 22 patients managed with careful deairing procedures had persistence of air bubbles for at least 30 minutes and usually for 45 minutes. In 56 patients with CO2 field flooding, all foam disappeared in less than 1 minute in 48 patients and the remaining 8 had complete disappearance in 1 to 24 minutes. These observations demonstrate the ineffectiveness of the usual deairing maneuvers and the effectiveness of CO2 field flooding in displacing air.     

UV-B and the immune system. A review with special emphasis on T cell-mediated immunity

The immunosuppressive activity of ultraviolet light-B (UV-B) has become a major topic of interest, especially now that there are indications of an increased exposure to UV-B on the earth's surface, caused by a decreased thickness of the ozone layer. This review indicates that the thymus-dependent immune system is a prime target for damage by UV-B. Especially the systemic effects of UV-B on T cell mediated immunity are described and analyzed with respect to the mode of action. In summary, this review demonstrated that UV-B can alter T cell mediated immune responses by different pathways in which cytokines (e.g. TNF-alpha) and other soluble mediators (e.g. cis-urocanic acid) may play a role. Effects of UV-B on the location and morphology of different cells in the skin affect functionality of the immune system. Thus, UV-B may suppress local immunity against skin tumours and skin-associated infections as well as systemic immunity against non skin-associated infectious diseases and tumours.     

Fibrin regulates neutrophil migration in response to interleukin 8, leukotriene B4, tumor necrosis factor, and formyl-methionyl-leucyl-phenylalanine

We have examined the capacity of four different chemoattractants/cytokines to promote directed migration of polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of extracellular matrix proteins. About 20% of PMN migrated through fibrin gels and plasma clots in response to a gradient of interleukin 8 (IL-8) or leukotriene B4 (LTB4). In contrast, < 0.3% of PMN migrated through fibrin gels in response to a gradient of tumor necrosis factor alpha (TNF) or formyl-methionyl-leucyl-phenylalanine (FMLP). All four chemoattractants stimulated PMN to migrate through gels composed of collagen IV or of basement membrane proteins (Matrigel), or through filters to which fibronectin or fibrinogen had been adsorbed. PMN stimulated with TNF or FMLP adhered and formed zones of close apposition to fibrin, as measured by the exclusion of a 10-kD rhodamine-polyethylene glycol probe from the contact zones between PMN and the underlying fibrin gel. By this measure, IL-8- or LTB4-treated PMN adhered loosely to fibrin, since 10 kD rhodamine-polyethylene glycol permeated into the contact zones between these cells and the underlying fibrin gel. PMN stimulated with FMLP and IL-8, or FMLP and LTB4, exhibited very little migration through fibrin gels, and three times as many of these cells excluded 10 kD rhodamine-polyethylene glycol from their zones of contact with fibrin as PMN stimulated with IL-8 or LTB4 alone. These results show that PMN chemotaxis is regulated by both the nature of the chemoattractant and the composition of the extracellular matrix; they suggest that certain combinations of chemoattractants and matrix proteins may limit leukocyte movements and promote their localization in specific tissues in vivo.     

Measurements of exit rates to distinguish between facilitated and simple diffusion

A modification of the method of Sen and Widdas (J. Physiol. London 160:392-403, 1962) was used to measure the rate of exit of several nonelectrolytes from erythrocytes of various species. In spite of additional errors introduced by the larger half-saturation values of the carriers (phi) and concentrations, it was possible to distinguish between systems with small values of phi, systems with relatively large values of phi, and systems involving only simple diffusion. Approximate values of phi in millimoles and of maximum transfer rate (K) in isotonic units per minute were obtained using times and initial slopes measured on experimental curves. The following values in the foregoing units were obtained: human glucose, phi = 1.8, 1.0, K = 0.8, 1.1; human glycerol, phi = 178, 94, K = 4.3, 3.3; sheep thiourea, phi = 56, 56, K = 0.9, 0.6; and rabbit glycerol, phi = 328, 64, K = 2.2, 1.0. Simple diffusion was demonstrated for the following systems: ox-ethylene glycol; ox-glycerol; sheep-ethylene glycol; and sheep glycerol.     

Action potential characteristics of rabbit papillary muscle

The ionic components of the action potential (AP) in rabbit right papillary muscle (RRPM) were determined by simple methods such as changes in external concentrations of sodium and calcium ions and addition of MnCl2 ot the perfusion fluid. Two components (fast and slow) were clearly visible in the upstroke of AP in normal Tyrode solution. MnCl2 (5 mmol/l) eliminated the slow component which forms the overshoot (OS) leaving the fast one unaffected, indicating that the former was related to a slow inward current. Mn also drastically reduced AP duration without changing the slope of phase 3 of repolarization. Reduction of Na concentration to 90 mmol/l did not affect the peak voltage of the OS but shortened AP. This low-Na solution reduced both (Vmax)f and the amplitude of the fast component. Ca-free solution reduced OS and increased AP duration. In high-Ca Tyrode (7.2 mmol/l) OS was increased and AP shortened. The effects of MN were reversed in this solution. The results suggest that the upstroke of the RRPM action potential is determined by two different ionic currents: a fast Na current responsible for the fast component and a slow inward current carried mainly by Ca, this latter being responsible for the slow component in the upstroke and for the plateau phase. The existence of propagated, Ca-dependent slow responses was demonstrated. Emphasis is placed on the fact that the major determination of the repolarization process in this type of AP is probably the inactivation of the slow inward Ca current.