We have studied the interaction of CapZ, a barbed-end actin capping protein from the Z line of skeletal muscle, with actin. CapZ blocks actin polymerization and depolymerization (i.e., it "caps") at the barbed end with a Kd of approximately 0.5-1 nM or less, measured by three different assays. CapZ inhibits the polymerization of ATP-actin onto filament ends with ATP subunits slightly less than onto ends with ADP subunits, and onto ends with ADP-BeF3- subunits about as much as ends with ADP subunits. No effect of CapZ is seen at the pointed end by measurements either of polymerization from acrosomal processes or of the critical concentration for polymerization at steady state. CapZ has no measureable ability to sever actin filaments in a filament dilution assay. CapZ nucleates actin polymerization at a rate proportional to the first power of the CapZ concentration and the 2.5 power of the actin concentration. No significant binding is observed between CapZ and rhodamine-labeled actin monomers by fluorescence photobleaching recovery. These new experiments are consistent with but do not distinguish between three models for nucleation proposed previously (Cooper & Pollard, 1985). As a prelude to the functional studies, the purification protocol for CapZ was refined to yield 2 mg/kg of chicken breast muscle in 1 week. The activity is stable in solution and can be lyophilized. The native molecular weight is 59,600 +/- 2000 by equilibrium ultracentrifugation, and the extinction coefficient is 1.25 mL mg-1 cm-1 by interference optics. Polymorphism of the alpha and beta subunits has been detected by isoelectric focusing and reverse-phase chromatography. CapZ contains no phosphate (less than 0.1 mol/mol).

Chicken muscle CapZ, a member of the capping protein family of actin-binding proteins, binds to the barbed end of actin filaments and nucleates actin polymerization. No regulation of the capping protein family has been described. We report that micelles of phosphatidylinositol 4,5-bisphosphate (PIP2) bind to CapZ and completely inhibit its ability to affect actin polymerization as measured by several independent assays. Higher concentrations of other anionic phospholipids also completely inhibit the activity of CapZ. Neutral phospholipids have no effect. Mixed vesicles of PIP2 with phosphatidylcholine or phosphatidylethanolamine also inhibit CapZ, but addition of Triton X-100 both prevents and reverses PIP2's inhibition of CapZ.

The lack of reliable methods for minimally invasive biopsy of suspicious enhancing breast lesions has hindered the utilization of contrast-enhanced magnetic resonance imaging (MRI) for the detection and diagnosis of breast cancer. In this study, a freehand method was developed for large-gauge core needle biopsy (LCNB) guided by intraprocedural MRI (iMRI). Twenty-seven lesions in nineteen patients were biopsied using iMRI-guided LCNB without significant complications. Index terms: breast biopsy; breast neoplasms; core needle biopsy; interventional; magnetic resonance imaging THE EMERGENCE OF CONTRAST-ENHANCED BREAST MAGNETIC RESONANCE IMAGING (MRI) as a sensitive means of detecting radiographically occult breast cancer is precipitating an increasing number of breast MRI scans every year. As more scans are performed, more enhancing lesions are being discovered that merit biopsy. The primary method for sampling MRI-detected lesions remains preoperative MRI-guided needle localization (either stereotaxic (1-3) or freehand (4,5)) and hookwire placement followed by surgical biopsy. Surgical biopsy is costly, invasive, and affects the cosmetic appearance of the breast. The purpose of this study was to develop a nonsurgical method for minimally invasive large-gauge core needle biopsy (LCNB) of enhancing breast lesions using direct, intraprocedural MRI (iMRI) guidance. We report our experience using a freehand iMRI-guided LCNB method that is based on a previously described method for preoperative needle localization and lesion marking (4). MATERIALS AND METHODS Patient PopulationThe study population consisted of 19 patients, ranging from 33 to 67 years old, who underwent iMRI-guided LCNB between May 14, 1998 and November 3, 1999. Two patients had three lesions each, four patients had two lesions each, and 13 patients had one lesion each, for a total of 27 biopsied lesions. Lesion diameter ranged from 0.5 to 4.0 cm (average 1.8 cm) on preliminary diagnostic MRI. Six lesions were 1 cm or less; 12 lesions were 1-2 cm; six lesions were 2-3 cm; three lesions were 3-4 cm. To facilitate rapid recruitment for this feasibility study, any patient with a suspicious lesion visible on previous diagnostic MRI was eligible for the study, regardless of whether the lesion could have been biopsied by other means, such as under mammographic or sonographic guidance. Lesions were considered suspicious if any of the imaging modalities or physical exam indicated biopsy. On MRI, focal lesions with rapid initial enhancement on dynamic imaging or abnormal morphology on high-resolution imaging were considered suspicious. Seven lesions were mammographically visible. Seven lesions were palpable. Fifteen lesions, four of which were sonographically visible, were imaged with ultrasound. All patients gave their signed informed consent in accordance with our institutional panel on human subjects.

There has been continued development of MRI techniques for evaluating mesenteric vascular disease. Contrast-enhanced magnetic resonance angiography (MRA) can provide reproducible high resolution, high contrast images of the arterial and venous mesenteric vasculature and may allow detection of segmental ischemia by detection of segmental delayed mesenteric or bowel wall enhancement. Cine phase-contrast MRA can provide additional information about the rate and volume of flow within the major mesenteric arteries and veins. Real-time MRI can provide interactive visualization of the mesenteric vessels in any plane, and with suitable bowel contrast, it can be used to monitor global and segmental small bowel motility. With in vivo MR oximetry, flow independent measurements of the T2 relaxation of blood allow the oxygen saturation of the mesenteric circulation to be determined. These MR techniques can be combined for evaluating both anatomic and functional aspects of the mesenteric circulation.

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