129 Gen. Physiol. Biophys. (2010), 29, 129–133 doi:10.4149/gpb_2010_02_129 Analysis of rat papillary muscle transverse deformation by laser difraction Adolfo Virgen-Ortiz 1 , Alejandro Apolinar-Iribe 2 , Martín E. Ríos-Martínez 3 , José L. Marín 4 and Jesús Muñiz 3 1 Departamento de Ciencias Químico Biológicas y Agropecuarias, División de Ciencias e Ingeniería, Unidad Regional Sur, Universidad de Sonora. Blvd. Lázaro Cárdenas No. 100, Colonia Francisco Villa, CP 85880, Navojoa, Sonora, México 2 Departamento de Física, Universidad de Sonora, Apdo. Postal 1626, CP 83000, Hermosillo, Sonora, México 3 Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de Julio No. 965, Col. Villas San Sebastián, CP 28040, Colima, Colima, México 4 Departamento de Investigación en Física, Universidad de Sonora, Apdo. Postal 5-088, CP 83190, Hermosillo, Sonora, México Abstract. We use laser difraction in the analysis of the transversal deformation that the papillary muscle of the female and male Wistar rat may undergo when is subjected to diferent tension (tension range, 0–30 mN) in the longitudinal plane. Papillary muscles from the right ventricle were illuminated at normal incidence with a He-Ne laser lasing at 594 nm at room temperature. he far-ield difraction pattern projected to a screen was recorded with a digital camera for its analysis. he analysis of the stress-strain curves from the two experimental groups shows that the papillary muscles from male rats exhibit a higher stifness in the transversal axis compared to the female rats. Key words: Cardiac papillary muscle — Transverse deformation — Laser difraction Correspondence to: Alejandro Apolinar-Iribe, Departamento de Física, Universidad de Sonora, Apdo. Postal 1626, CP 83000 Her- mosillo, Sonora, México E-mail: apolinar@ciencias.uson.mx Introduction Papillary muscles play a vital role in the pumping ef- ficiency of the heart. These cylindrically shaped muscles are attached at one end to the wall of the left or the right ventricle and at the other end to the mitral or tricuspid valve, respectively. During ventricular systole, the increas- ing pressure in the ventricles tends to push the valves upward into the atria, which would allow backflow of blood during ejection. The papillary muscles prevent this inversion by contracting and holding the valves closed. Due to their relatively simple geometry and muscle fib- ers aligned along their axes, papillary muscles have been popular in studies of the passive and active mechanical properties of heart muscle. For determining normal and shear properties, combined extension and torsion is a useful loading protocol (Taber 2004). Both in human and animal models it has been observed that there are structural and functional diferences in the female and male heart, and the understanding of these variations can be clinically important to elucidate the progress until a pathophysiological study is obtained. In the case of animals, it is known that the heart size is greater in male rats than in female rats, nevertheless the heart weight/body weight ratio is greater in females than in males (Capasso et al. 1983; Leblanc et al. 1998). Also, there have been reported diferences in the contractility, for example, the papillary muscle of a male rat develops higher tension than females up to ages 6–14 months, and there are not signiicant diferences observed in the cross sectional area of papillary muscle removed from the let ventricle (Leblanc et al. 1998). Recently, it has been reported that there are electrophysiological diferences between male and female, especially in the electrocardiographical pattern of ventricular repolarisation. Females may have lengthening of the QT interval (time from electrocardiogram Q wave to the end of the T wave), when increased QT is observed, females are more susceptible to development polymorphic ventricular tachycardia (Abi-Gerges et al. 2004). Moreover, other aspect of relevance is the deformation of cardiac tissues. here are