Lack of evidence for functional natriuretic peptide receptors in the heart of the cane toad, Bufo marinus.
Several studies have shown that the heart of species from each vertebrate class contains natriuretic peptide binding sites which suggests that ANP released from the heart may act in a paracrine/autocrine fashion. The present study used a set of techniques to study cell surface receptors in order to investigate the presence and nature of NPRs in the heart of the cane toad, Bufo marinus. Autoradiographical studies of both atria and ventricle showed no variation between total and non-specific binding, indicating a lack of NP binding sites in these tissues. This was confirmed with in vitro binding studies in which increasing concentrations of ANP did not compete for any specific binding. Increasing concentrations of ANP did not increase cGMP generation and physiological experiments showed that both ANP and CNP had no effect on the force or rate of contraction of a sino-atrial preparation. Molecular expression studies, however, showed that mRNA for NPRs was expressed in the heart, in spite of the lack of evidence for NPR on the cell surface. Overall, this study showed that no functional NPRs are present in the heart, and provided evidence that the heart is not a target organ for NP action in B. marinus.
Minerds
K L
KL
School of Biological and Chemical Sciences, Deakin University, Geelong, Victoria, Australia. kilm@deakin.edu.au
Donald
J A
JA
D000818:Animals; D001345:Autoradiography; D002024:Bufo marinus / Q000502:physiology*; D006152:Cyclic GMP / Q000378:metabolism; D005786:Gene Expression Regulation; D006162:Guanylate Cyclase / Q000032:analysis; D006325:Heart Atria / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism*; D066298:In Vitro Techniques; D020098:Natriuretic Peptide, C-Type; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D017461:Receptors, Atrial Natriuretic Factor / Q000235:genetics / Q000378:metabolism*
D011506:Proteins; D020098:Natriuretic Peptide, C-Type; D006162:Guanylate Cyclase; D017461:Receptors, Atrial Natriuretic Factor; D006152:Cyclic GMP