SUMMARY1. The subcellular composition of relaxed and noradrenaline-contracted rabbit main pulmonary artery smooth muscle cells was measured by electron probe X-ray microanalysis of cryosections of rapidly frozen tissue. Some of the preparations were made permeable with saponin and exposed to a known free Ca ion concentration, rapidly frozen, freeze-substituted, and also analysed by electron probe X-ray microanalysis.2. 98 % of intracellular K could be replaced by Rb. This was done to remove the K peak that partially overlaps the Ca peak in the X-ray spectra. 8. Mitochondrial [Ca] was not significantly different in relaxed and contracted tissues (P > 0-05). Mitochondrial [Ca] was 2-2 + 0-24 mmol/kg dry wt. (mean + S.E. of mean; n = 163), combining data from relaxed and contracted tissues. K was replaced by Rb in mitochondria to the same extent as in the cytoplasm.9. In saponin-treated preparations exposed to 1 AM-free Ca ions and 5 mM-oxalate, the s.r. lumen was swollen and contained Ca deposits. These deposits occurred at sites apposed as well as not apposed to the plasma membrane (junctional and central s.r.), amidst cytoplasm that contained little Ca by comparison. Large deposits of calcium oxalate adjacent to the nucleus were frequently observed, in a distribution similar to that of the Golgi apparatus.10. We conclude that: (a) the central s.r. can accumulate large amounts of Ca, (b) noradrenaline releases Ca from the central s.r., as well as from the junctional s.r., (c) noradrenaline releases Ca from the central s.r. in the presence of normal (1 2 mM) extracellular Ca, (d) the release of Ca from central s.r. is sufficient to cause maximal contraction, (e) the relative sizes of the central s.r. and mitochondrial Ca pools in relaxed tissue are about 20: 1.
Filamentous myosin is present in both relaxed (myosin light chains unphosphorylated) and contracted (light chains phosphorylated) vascular smooth muscle. The organization of myosin and actin filaments and the insertion of the latter on cytoplasmic and plasma membrane bound dense bodies is consistent with a mini sarcomere-like organization and a sliding filament mechanism of contraction in smooth muscle. Mitochondria are high capacity, low affinity Ca stores in smooth muscle. They do not play a role in the regulation of cytoplasmic Ca2+ at physiological levels. The localization and Ca content of the junctional sarcoplasmatic reticulum (SR) is consistent with this organelle being the major intracellular source of activator Ca released by excitatory transmitters. Repeated contractions in the absence of extracellular Ca2+ (thought to represent recycling of intracellular activator Ca2+) can be demonstrated if the excitatory agent is not allowed to remain in contact with the smooth muscle throughout relaxation.; the demonstration of "recycling" is facilitated if the efflux of cellular Ca2+ is blocked. The rise in total cytoplasmic calcium measured with electron probe analysis during a maintained (30 min) contracture in rabbit portal-anterior mesenteric vein smooth muscle (approximately 0.9 mol/kg dry cytoplasm) is greater than the amount of Ca that could be bound to calmodulin.
Blood glucose levels were measured over a 24-h period in eight insulin-dependent diabetic subjects who were difficult to control and who presented with morning fasting hyperglycemia. At least seven exhibited clinical characteristics suggestive of the Somogyi phenomenon. A continuous glucose monitoring apparatus was used to relate the concentrations of glucose during the day to concomitant levels of free insulin and cortisol. In all patients a significant (P < 0.01) rise in fasting morning glucose started at about 0600 h, while they were still asleep. In six patients the morning elevation of blood glucose was preceded by stable, almost normal glucose levels during the night (117 ± 2.5 mg/dl); one of the two remaining patients (no. 7) exhibited high overnight glucose levels (268 ± 7 . 2 mg/dl), whereas the other (no. 8) had a mild hypoglycemic episode (45 mg/dl) 6 h before the hyperglycemic period.In all patients the fasting glucose rise was associated with the usual morning cortisol surge (P < 0.05)and with a significant decrease in the concentration of serum free insulin (P < 0.01). The free insulin levels in patient no. 8 were higher, while those of patient no. 7 were lower, than in the other six patients. We conclude that the diurnal morning rise in cortisol may cause hyperglycemia in insulin dependent diabetic patients if insufficient exogenous insulin remains and/or endogenous insulin is not secreted. In such patients the high levels of fasting glucose in the morning may misrepresent their overnight control of blood glucose and lead to an erroneous impression of the Somogyi phenomenon.
An intelligent interface has been designed to perform synchronous digital image acquistion and scan generation (SDIASG interface) for a microprocessor controlled Scanning Transmission Electron Microscope (S(T)EM) with x‐ray imaging. The SDIASG interface connects an LSI‐11/2 microprocessor to a Philips EM400 electron microscope. The LSI‐11/2 microprocessor is part of a DeAnza VC5000 digital image display system. A system using the SDIASG interface is described. The system takes advantage of the SDIASG interface and a DeAnza VC5000 digital image display system to realize new capabilities that optimize conditions for x‐ray mapping. A low characteristic x‐ray count rate is generated by the ultrathin specimens from which high resolution x‐ray maps can be obtained (Shuman et al, 1976; Somlyo and Shuman, 1982). This low count rate necessitates a long image accumulation time, which in turn makes drift correction essential for maintaining spatial resolution. The new capabilities of the system described here consist of real‐time display and summation of consecutive image and x‐ray maps, and automatic return to a high speed imaging mode between consecutive x‐ray map passes. The new capabilities combine to allow frequent correction for specimen drift between consecutive x‐ray mapping passes while still permitting a long total accumulation time for the x‐ray maps.
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