Background and Purpose-To explore relationships among gender, body size, neck size, and the diameters of the common carotid artery (CCA) and internal carotid artery (ICA). Methods-Using multivariate regression, the best predictors of sonographic diameters of CCA and ICA were determined based on age, height, weight, body mass index, body surface area, neck circumference, neck length, and blood pressure. Results-Measurements were obtained in 500 consecutive patients (age 52Ϯ15 years; 61% women). Mean diameters of ICA (4.66Ϯ0.78 mm) and CCA (6.10Ϯ0.80 mm) in women were significantly smaller than in men: 5.11Ϯ0.87 mm and 6.52Ϯ0.98 mm, respectively. Sex significantly influenced the diameters after controlling for body size, neck size, age, and blood pressure. Conclusions-Carotid arteries are smaller in women even after adjusting for body and neck size, age, and blood pressure.

The purified saxitoxin (STX) binding component of the rat sarcolemmal sodium channel (SBC) has been reconstituted into phospholipid vesicles. The reconstituted SBC displays the pharmacological properties and the ability to control sodium fluxes expected of a functional sodium channel. Batrachotoxin (BTX) increases 22Na' influx into reconstituted SBC vesicles by >100% over control at early time points. The BTX-stimulated 22Na' influx is specifically and quantitatively blocked by STX. Veratridine and aconitine also stimulate Na+ flux-although less effectively than BTX-in the order: BTX > veratridine > aconitine. The logarithmic dose-response curves for BTX and veratridine are sigmoidal with a K0.5 of 1.5 ,M and 35 ,uM, respec-tively. Vesicles containing the reconstituted SBC demonstrate 3H-labeled STX binding to a single class of high affinity sites with a kd of 5-7 nM at 0°C; the thermal stability of the STX receptor is markedly enhanced by reconstitution. Our results confirm that the purified STX binding component from rat sarcolemma constitutes the sodium channel itself and contains at least those components sufficient for channel activation, transmembrane ion movement, and inhibition by STX.The action potential in excitable membranes typically arises from rapid and transient voltage-dependent increases in membrane permeability to Na+ and K+ (1). These permeability changes are produced by separate, ion-selective channels that are believed to be formed by integral proteins that span the bilayer to provide gated polar pathways for cation movement (2). Recently, rapid progress has been made in the solubilization and purification of components of the voltage-dependent sodium channel. This effort has been aided by the availability of neurotoxins that interact specifically with the channel in a manner that can be defined both electrophysiologically and biochemically (3).Radiolabeled saxitoxin (STX) and tetrodotoxin (TTX) have been used to detect sodium channel components solubilized in non-ionic detergents, and a solubilized STX/TTX binding protein has been purified from eel electroplax (4), rat synaptosomes (5), and rat skeletal muscle sarcolemma (6). Prior to this report, the question of whether these purified proteins were intact sodium channel complexes, and whether they survived solubilization and purification in a functional form, remained unanswered.Several groups have reported reconstitution of unpurified sodium channels into lipid vesicles after partial disruption or complete solubilization of nerve membranes in sodium cholate (7-10). In most studies, crude membrane fragments or solubilized membrane preparations were used for reconstitution and no preliminary fractionation procedures were performed. We report here the successful reconstitution of a purified mammalian sodium channel protein. (11) and stored at -60'C. The LiBr extraction solution contained 1 mM iodoacetamide, 0.1 mM phenylmethylsulfonyl fluoride, pepstatin at 0.1 ,ug/ml, and 0.2 mM EGTA. Solubilization and purification of the SBC wer...

SUMMARY1. The characteristics of saxitoxin (STX) binding to the mammalian Na channel have been studied in purified sarcolemma isolated from rat skeletal muscle.2. STX binds specifically to isolated sarcolemma with a Kd of 1*43 x 10-9 M and Bmax of 7-8 p-mole STX bound/mg membrane protein at 0C in the presence of 140 mM-NaCl. 3. Denervation (10-14 days) results in a 43 % reduction in the density of highaffinity STX binding sites in purified sarcolemma, but the 1Kd for this class of sites is not changed.4. In sarcolemma, the apparent Kd for STX binding is dependent on temperature, pH and ionic strength. The Q10 for Kd between 0 and 40 0C is 1P3. Protonation of a group having a pK of 6*0 markedly raises Kd without affecting Bmasx. Apparent Kd increases eightfold when ionic strength is raised from 20 to 600 mM. 5. Dissociation and association rate constants for STX binding are temperature dependent with Q10 of 2-6 and 1-9 respectively between 0 and 20 'C.6. STX binding is competitively inhibited by monovalent and divalent cations under conditions of constant total ionic strength. An affinity sequence of Tl+ > Li+ > Na+ > K+ > Rb+ > Cs+ is seen for the monovalent cation-binding site.7. The STX binding site is relatively stable to heat and to enzymic degradation. A specific modifier of carboxyl residues inactivates subsequent STX binding. This process can be prevented by the presence of STX during the reaction.8. Characteristics of the STX binding site in isolated sarcolemma are compared to those reported for other isolated excitable membranes and for studies of whole muscle and muscle homogenate. Sarcolemma provides a potential source of enriched Na channels for further purification efforts in a mammalian system.