An Electron Microscope Study of Smooth Muscle in Pregnant Uterus of the Rabbit

In the smooth muscle of the rabbit uterus one type of myofilament can be found; this is about 50 A thick. In the sarcoplasmic reticulum there are smooth walled vesicles and many vesicles with particles attached. It is suggested that these particles may correspond to the ribonucleoprotein-containing particles of Palade and Siekevitz. The diameter of the particles is 250 A. There are also unattached particles some of which may be glycogen. The membranes of the muscle cells and the connective tissue lying between them are described.     

Action of Certain Tropine Esters on Voltage-Clamped Lobster Axon

Tropine p-tolylacetate (TPTA) and its quaternary analogue, tropine p-tolylacetate methiodide (TPTA MeI) decrease the early transient (Na) and late (K) currents in the voltage-clamped lobster giant axon. These agents, which block the nerve action potential, reduce the maximum Na and K conductance increases associated with membrane depolarization. They also slow the rate at which the sodium conductance is increased and shift the (normalized) membrane conductance vs. voltage curves in the direction of depolarization along the voltage axis. All these effects are qualitatively similar to those resulting from the action of procaine on the voltage-clamped axon. One unusual effect of the tropine esters, noticeable particularly at large depolarization steps, is that they cause the late, K current to reach a peak and then fall off with increasing pulse duration. This effect has not been reported to occur as a result of procaine action. Tropine p-chlorophenyl acetate (TPClA), which differs from TPTA only by the substitution of a p-Cl for a p-CH₃ group on the benzene ring, had a negligible effect on axonal excitability.