Preoperative balloon occlusion: “the intravascular ligature”

The resection of cerebral arteriovenous malformations may be difficult or very hazardous when access to the feeding arteries is limited by overlying large draining veins. Properative occlusion of feeding arteries can be performed using detachable flow-directed balloons.     

Platelet attachment and spreading on polystyrene surfaces: dependence on fibronectin and plasma concentration

Fibronectin promoted platelet attachment and spreading on polystyrene surfaces but was not essential if the surfaces were coated with plasma. The dependence of platelet adhesion on plasma concentration was complex. The extent of attachment and spreading was increased on surfaces treated with up to 1.0% plasma and decreased at higher plasma concentrations. The results support the hypothesis that protein adsorption is not directly related to protein concentration when surfaces are exposed to complex protein mixtures.     

Radiology of acute subtemporal subdural hematomas

Four cases of acute subtemporal hematoma are presented. The diagnostic appearance of this lesion on axial and coronal computed tomographic (CT) scans and at angiography is described.     

Contribution of presynaptic calcium-activated potassium currents to transmitter release regulation in cultured Xenopus nerve-muscle synapses

Using Xenopus nerve-muscle co-cultures, we have examined the contribution of calcium-activated potassium (K(Ca)) channels to the regulation of transmitter release evoked by single action potentials. The presynaptic varicosities that form on muscle cells in these cultures were studied directly using patch-clamp recording techniques. In these developing synapses, blockade of K(Ca) channels with iberiotoxin or charybdotoxin decreased transmitter release by an average of 35%. This effect would be expected to be caused by changes in the late phases of action potential repolarization. We hypothesize that these changes are due to a reduction in the driving force for calcium that is normally enhanced by the local hyperpolarization at the active zone caused by potassium current through the K(Ca) channels that co-localize with calcium channels. In support of this hypothesis, we have shown that when action potential waveforms were used as voltage-clamp commands to elicit calcium current in varicosities, peak calcium current was reduced only when these waveforms were broadened beginning when action potential repolarization was 20% complete. In contrast to peak calcium current, total calcium influx was consistently increased following action potential broadening. A model, based on previously reported properties of ion channels, faithfully reproduced predicted effects on action potential repolarization and calcium currents. From these data, we suggest that the large-conductance K(Ca) channels expressed at presynaptic varicosities regulate transmitter release magnitude during single action potentials by altering the rate of action potential repolarization, and thus the magnitude of peak calcium current.