Secretory polymorphism and serous cutaneous gland heterogeneity in Bufo granulosus (Amphibia, Anura)

Three types of secretory products (a, b and c) in the poison glands of the Argentine toad Bufo granulosus have been detected under light microscope. T he type a secretory product consists of granules of homogeneous density, ty pe b of vesicles with a translucent compartment and type c of granules of v arying density. Subsequent transmission electron microscope analysis disclo sed obvious similarities in the secretory pathways of type a and c granules ; the differences detected under light microscope are due to the functional phases observed. On the contrary, production of type b secretory vesicles involves a distinctive pathway. Therefore, two classes of glands (I and II) have been identified. Glands of the first class are typical of bufonid toa ds and produce granules provided with repeating substructure; glands of the second class, which manufacture a lucent product, are unusual in the famil y Bufonidae. Ultrastructural differences, consistent with the two gland cla sses, have also been described in the myoepithelia. The myocytes ensheathin g class I secretory units possess striking cytoskeletal specializations, wh ereas those of class IT glands an rich in sarcoplasmic reticulum. The disti nctive ultrastructural traits detected in these myoepithelial cells have be en compared with the results of previous studies on the dimorphic serous gl ands of Bombina. Findings point to the use of pharmacological treatment on the skin of anurans with different classes of serous glands to elicit diffe rential secretory discharge. (C) 1999 Elsevier Science Ltd. All rights rese rved.