Application of the electron microscope to the cytochemical peroxidase reaction in salamander leukocytes

Electrophysiological properties of three types of granulocytes in circulating blood of the newt

1. The electrophysiological properties of three subtypes of granulocytes obtained from the circulating blood of the newt, Triturus pyrrhogaster, were studied using the whole-cell variation of the patch-electrode voltage-clamp technique. 2. Neutrophils were identified by their multilobulated nucleus in the cytoplasm. Basophils and eosinophils, having characteristic granular structures in their cells, could definitely be distinguished from other leucocytes. The reliability of cellular identification using phase-contrast microscopy was confirmed by fixing and staining the granulocytes with Wright's solution. 3. In neutrophils under current-clamp conditions, a hyperpolarization-induced conductance increase was observed. With depolarization, however, no changes in regenerative potential were detected. When voltage clamped in standard saline (containing 96 mM-NaCl), hyperpolarizing voltage pulses to a potential more negative than -90 mV evoked slowly decaying inward currents. 4. The hyperpolarization-evoked membrane currents in neutrophils were identified as anomalous rectifying K+ currents, since (1) externally applied Cs+ (0.1 or 1 mM) or Ba2+ (1 mM) produced suppressive effects on the currents, (2) replacement of external Na+ with choline ions eliminated the decay of macroscopically observed currents, and (3) both the amplitude and kinetic properties of the currents were strongly dependent on membrane potential as well as on external K+ concentration; the activation of the conductance depended on the electrochemical force for K+ rather than on membrane potential alone. The magnitude of steady-state conductance was roughly proportional to the square root of the external K+ concentration. 5. In basophils and eosinophils, no major time- or voltage-dependent increase in conductance was detected at voltages between +20 and -130 mV. However, under current-clamp conditions, spontaneous fluctuation of zero-current potentials was clearly apparent, presumably due to the activities of some ion channels generating a small amount of current flux through the membranes of these cells. 6. It was concluded that the three subtypes of granulocytes in the newt differ considerably not only in appearance and structure but also in the electrical properties of their membranes. The anomalous rectifying K+ channels in neutrophils may serve to determine the resting potential of the cell at K+ equilibrium potential. The closure of the channels at depolarization might facilitate the maintenance of depolarization triggered by stimuli accompanying current influx.

A study of the T system in rat heart

The technique of extracellular space tracing with horseradish peroxidase is adapted for labeling the transverse tubular system (T system) in rat heart. In rat ventricular muscle the T system shows extensive branching and remarkable tortuosity. The T system can only be defined operationally, since it does not display specific morphological features throughout its entire structure. Owing to branching of the T system, a sizable proportion of the apposition between the T system and L system (or closed system) occurs at the level of longitudinal branches of the T system and is not restricted to the Z line region. The regions of apposition between the T system and L system are analyzed in rat ventricular muscle and skeletal muscle (diaphragm) and compared with the intercellular tight junctions (nexuses) of heart muscle by the use of a photometric method. The over-all thickness of the nexus is significantly smaller than that of T-L junctions in both cardiac and skeletal muscles. The thickness of the membranes of the T and L systems are not significantly different in the two muscles, but the gap between both membranes is larger in the heart. In atrial muscle the following two types of cells are found: (a) those cells with a well-developed T system in which the tubular diameter is quite uniform and the orientation predominantly longitudinal and, (b) cells with no T system, but with a well-developed L system. Atrial cells possessing a T system are richly provided with specific granules and show little micropinocytotic activity, whereas cells devoid of T system show intense micropinocytotic activity and few specific granules. The possible functional implications of these findings are discussed.