Some observations on intrinsic cardiac rate regulation in several marine vertebrates

Abstract

1. 1. A pressure-sensitive intrinsic cardiav rate regulatory mechanism has been demonstrated in the hearts of six species of marine fishes. These were: the rockfishes, Sebastes miniatus, Sebastodes constellatus, and S. paucispinis; the sablefish, Anoplopoma fimbria; the blue shark, Prionace glauca; and juvenile, recently metamorphosed Dover sole, Microstomus pacificus. 2. 2. These data extend and confirm earlier findings that an intrinsic cardiac rate regulatory mechanism is present in the hearts of elasmobranch and teleostean fishes and lend additional support to the concept that this mechanism represents an ancient and independent phylogenetic development in many species of organisms. These findings are particularly significant as they were obtained on specimens collected from both pelagic and bathypelagic regions of the ocean. 3. 3. These data, together with the results obtained from similar studies on the hearts of a number of other fishes, clearly indicate that the phenomenon of intrinsic cardiac rate regulation is of general occurence in the hearts of members of the classes Cyclostomata, Chondrichthyes, and Osteichthyes.