Tonus Waves From the Sinoauricular Muscle Preparation of the Terrapin as Affected by Adrenalin

Smooth Muscle in Cardiac Chambers is Common in Turtles and Extensive in the Emydid Turtle,Trachemys scripta

“…The atrial smooth muscle was particularly extensive in T. scripta , a species in the family (Emydidae) in which it was first described and detailed (Fano, ; Bottazzi, ; Gruber and Markel, ; Shaner, ). Although we only studied one Emydid species in our phylogenetic survey, the extensive functional data suggest that atrial smooth muscle is well developed across this family as tonus waves are prevalent in atrial preparations species in both major subfamilies (Emydinae, e.g., E. orbicularis ; Fano, ) (Deirochelyinae, e.g., T. scripta ; Joyce et al ., ).…”

“…In the late 19th century, slow wave contractions (the so‐called tonus waves) were observed in isolated atrial preparations from European pond turtles ( Emys orbicularis ) (Fano, ; Fano and Fayod, ; Bottazzi, ). The tonus waves were soon attributed to the conspicuous amounts of smooth muscle in the atria (Rosenzweig, ; Bottazzi, ), but despite a few decades of relatively intense research into its pharmacological properties (Fano, ; Fano and Fayod, ; Bottazzi and Grünbaum, ; Gault, ; Gruber and Markel, , ; Gruber, , , , ; Sollmann and Rossides, ; Gruber, ; Dimond, ), the scientific interest in the atrial smooth muscle waned after the 1920s. As part of other studies, we also observed the tonus waves (Galli et al ., ; Joyce et al ., ), and with a revived curiosity into their functional role, we recently demonstrated that the atrial smooth muscle may provide a powerful means to regulate ventricular filling and hence cardiac stroke volume (Joyce et al ., ).…”

“…The European‐based discoverers of the atrial smooth muscle universally employed the Emydid turtle E. orbicularis (formerly Emys europaea ) (e.g., Fano, ; Bottazzi and Grünbaum, ; Fano and Bodano, ; Rosenzweig, ; Oinuma, ), but were soon followed by North American studies on a wealth of other turtle species in the Emydid family, including Trachemys scripta (Laurens, ; Gruber and Markel, , ; Pereira, ; Sollmann and Rossides, ; Robb, ; Dimond, ). There are additional vague descriptions of tonus waves in atria from Chelydra serpentina (snapping turtles; Chelydridae); very little detail is given by Pereira (Pereira, ), where data are indiscriminately combined with findings in Emydid turtles, while Blinks and Koch‐Weser () cite their own unpublished observations about this species.…”