The mechanisms of conduction change depending on the extracellular K+ and Ca2+ concentrations ([K+]o and [Ca2+]o, respectively) were investigated. Simultaneous measurements of active and passive membrane properties and net membrane excitability were fulfilled by arranging the intra- and extracellular microelectrodes in a superfused and paced guinea pig papillary muscle. Internal longitudinal resistance (ri), as a parameter of passive property, was evaluated by the intra- and extracellular voltage ratio. The maximum upstroke rate (Vmax) was used as an active property. Apparent threshold potential (Vth) was defined by the breakpoint in the action potential upstroke fitted semilogarithmically. Graded rise in [K+]o (from 2.7 to 15.0 mM) evoked a progressive fall in Vmax, and was associated with less negative resting membrane potential and constant ri. Conduction velocity (theta) was the maximum in 9.0 mM [K+]o ("supernormal" conduction) but not in 2.7 mM [K+]o which gave the greatest Vmax ("subnormal" conduction). Safety factor of conduction (S), as an index of net excitability, could most readily account for the [K+]o-dependent change in theta. This was true also in the case of [Ca2+]o elevation (from 0.9 to 5.4 mM). These results indicate that the cation-modulated propagation is governed by the cable theory including S as a matrix of combined active and passive properties.
99Tcm-teboroxime is a new myocardial perfusion agent with a high first pass extraction and rapid myocardial washout. The usefulness of 99Tcm-teboroxime was evaluated for detection of myocardial ischaemia using a three-headed single photon emission tomography (SPECT) system which allows for rapid data acquisition. The subjects consisted of 14 patients, including seven with ischaemic heart disease, four with cardiomyopathy and three others. After the 99Tcm-teboroxime injection, dynamic data was collected every minute for 15 min with continuous rotation. High-quality SPECT images could be obtained by reconstructing the serial scans from 2 to 8 min. The sensitivity, specificity and accuracy of the 99Tcm-teboroxime study for the detection of the ischaemic region were not significantly different from those of the 201T1 study. Myocardial clearance was slow in the ischaemic lesion and in the myocardium of cardiomyopathy patients, while the coronary angiograms did not show any abnormality. These results therefore indicate that the rapid SPECT imaging and myocardial clearance of 99Tcm-teboroxime obtained with a three-headed SPECT system were useful for the detection of myocardial ischaemia.
The deformability of red blood cells (RBCs) is an important rheologic factor in the maintenance of normal blood flow in the microcirculation. Contrary to the well-known relationship between hyperlipidemia and atherosclerosis, the relationship between RBC rheology and the serum lipid profile has remained controversial and obscure. Moreover, the correlation of high-density lipoprotein (HDL)-cholesterol and RBC deformability has not been fully understood. In the present cross-sectional study of 139 apparently healthy subjects, we investigated whole-cell deformability (filterability) of RBCs in relation to the lipid profile, using a nickel mesh filter with 3.2-microm pores. RBC filterability was independent of gender, age and serum levels of low-density lipoprotein (LDL)-cholesterol. The filterability was significantly proportional to the HDL-cholesterol values (r = 0.382, p < 0.01), whereas it was inversely proportional to the triglyceride levels (r = -0.259, p < 0.01). These findings may provide new insight into the role of HDL-cholesterol not only in preventing atherosclerotic progression but also in improving RBC filterability.
