International Journal for Parasitology, Vol. 24, No. 4, pp. 551-562, 1994 Copyright © 1994 Australian Society for Parasitology Elsevier Science Ltd Printed in Great Britain. All rights reserved 0020-7519/94 $7.00+ 0.00 0020--7519(93)E0039-C EVIDENCE OF A MYOEPITHELIAL CELL IN TICK SALIVARY GLANDS LEWIS B. COONS,* CHARLES A. LESSMAN, MICHAEL w. WARD, R. HOWARD BERG and WILLIAM J. LAMOREAUX Department of Biology, Life Sciences Building, Memphis State University, Memphis, TN 38152, U.S.A. (Received 19 July 1993; accepted 29 November 1993) Abstract- COONS L.B., LESSMAN c. A., WARD M. W., BERG R.H. and LAMOREAUX w. J. 1994. Evidence of a myoepithelial cell in tick salivary glands. International Journal for Parasitology 24: 551-562. Type III acini from feeding female Dermacentor variabilis varied in size during in vitro and in vivo fluid production. As the type III acinus enlarged, its lumen enlarged and the adlumenal cell became thinner. As the acinus contracted, its lumen became smaller while the adlumenal cell became wider. Actin was demonstrated in salivary glands using an immunoblot technique. Actin was localized in the adlumenal cells of type III acini with fluorescent microscopy using rhodamine-phalloidin and with electron microscopy using heavy meromyosin to decorate actin filaments. Pre-treatment of salivary glands with cytochalasin D abolished fluorescence in adlumenal cells subsequently treated with rhodamine-phalloidin. These results support the hypothesis that the adlumenal cell in type III acini functions as a myoepithelial cell. INDEX KEY WORDS: tick; Ixodidae; Dermacentor variabilis, salivary gland; myoepithelial cell; adlumenal cell; salivary gland; fluorescence microscopy; electron microscopy. INTRODUCTION Ixoom ticks have a complex salivary gland. In females, three different types of acini are present, each with different kinds of cells (Till, 1959; Coons & Roshdy, 1973; Binnington, 1978; Fawcett, Doxsey & Buscher, 198la; 198lb). Type I acini help regulate water conservation when the tick is off the host (Needham, Rosell-Davis, Greenwald & Coons, 1990). Type II acini are thought to secrete pharmacologically active compounds into the host. Most likely, this secretion contributes only slightly to the total amount of fluid produced (Fawcett, Binnington & Voigt, 1986). Type III acini are the type most likely involved in fluid uptake from the hemolymph (Meredith & Kaufman, 1973; Fawcett et al., 1981b). During feeding, type III acini develop a large labyrinth characteristic of fluid transporting tissue (Coons & Lamoreaux, 1986; Fawcett et al., 1981a; Walker, Fletcher & Gill, 1985). The adlumenal cell in the type III acinus has been identified as a myoepithelial cell based on its ultrastructure (Krolak, Ownby & Sauer, 1982). There is 1 adlumenal cell per type III acinus *To whom all correspondence should be addressed. 551 (Walker et al., 1985; Coons & Lamoreaux, 1986; Coons & Kaufman, 1988). This cell connects to a bicuspid valve located at the junction of the salivary duct and the acinus (Coons & Lamoreaux, 1986). During feeding, the adlumenal cell in type III acini enlarges and many gap junctions develop with adjacent cells of the labyrinth (Fawcett et al., 1981a; Walker et al., 1985; Coons & Lamoreaux, 1986; Fawcett et al., 1986). Given the complexity of their salivary glands, it is not surprising that the feeding behavior of ixodid ticks is also complex. Ixodid ticks alternate feeding with salivation (Sweatman & Gregson, 1970; Gregson, 1973; Kemp, Stone & Binnington, 1982). With some variation, this cycle is repeated throughout host attachment. Females take up to 120 times their body weight in blood over a 9-13 day feeding period (Diehl, Aeschlimann & Obenchain, 1982). Most of the water and ions from this blood meal are returned to the host in a copious salivary secretion (Tatchell, 1967; 1969; Kaufman & Phillips, 1973a; 1973b; 1973c). This, in part, enables the tick to take such a large blood meal. Fluid uptake from the hemolymph of the tick into the lumen of the salivary gland acini is dependent on a dopamine activated cyclic AMP system (Kaufman, 1989; Sauer & Mcswain, 1992). It is not known how fluid moves out of the acini.