Toad

About: Toad is a research topic. Over the lifetime, 1624 publications have been published within this topic receiving 28732 citations.

Bufokinin: actions and distribution in the toad cardiovascular system.

Abstract: 1. Bufokinin is a substance P-like neuropeptide and potent spasmogen isolated from the intestine of the cane toad Bufo marinus. In the present study, we investigated the effects of bufokinin on systemic blood pressure and heart rate in the anaesthetized toad and the distribution of bufokinin-like immunoreactivity in the toad vasculature. 2. Intravenous bufokinin caused a dose-dependent fall in systemic blood pressure (maximum fall 20 mmHg) with an ED50 of 2.9 pmol. At higher doses, the effect was prolonged and blood pressure did not return to baseline within 60 min. There was no significant change in heart rate associated with hypotension. 3. Bufokinin-like immunoreactivity was mapped in whole mounts of toad blood vessels and organs using a mouse polyclonal antibody BK3 (at 1:5000) and the avidin-biotin method. Bufokinin-immunoreactive fibres were associated with most blood vessels examined: a moderately dense perivascular network of varicose fibres was present around renal arteries, with sparser immunoreactive fibres in the ventral aorta, sciatic artery, anterior abdominal vein and hepatic portal vein. 4. Bufokinin-immunoreactive fibres, mainly following blood vessels, were seen in whole mounts of the urinary/bladder and tongue, but not in the air sac. In the heart ventricle, varicose fibres were found in the valve cusps, intracardiac ganglia, epicardium and myocardium close to the endocardium, but not in the rest of the myocardium. 5. The vasodepressor action of bufokinin and the presence of bufokinin-like immunoreactivity in varicose fibres in various vessels suggest a role for bufokinin in haemodynamic regulation and/or sensory nerve function in the toad. The lack of any reflex tachycardia in response to the falls in blood pressure was of note.

Evidence for calmodulin dependence of water permeability in toad urinary bladder

Abstract: The calcium ion is an important intracellular regulator that mediates and modulates the actions of neurotransmitters and several hormones. Recent work from several laboratories has shown that many of calcium’s regulatory actions, in a wide variety of systems, are mediated by a single calcium-binding protein called calmodulin. Calmodulin is a calcium-dependent activator for a variety of cellular enzymes, including adenylate cyclase, cyclic nucleotide phosphodiesterase, and ( Ca2+Mg2+) -ATPase, as well as certain varieties of kinase.l The role of calcium in vasopressin’s action on toad bladder, however, is not yet clearly defined. Calcium ionophores have been shown to increase both basal water permeability and water permeability stimulated by low concentrations of vasopressin, while these ionophores inhibit the action of maximally stimulating concentrations of vasopressin.** 3 These studies point toward some role for calcium in modifying vasopressin’s action, but provide little firm evidence supporting any particular site of action for calcium. In an attempt to clarify these questions, we examined the effect of trifluoperazine (Stelazine), a drug that binds to calmodulin and inhibits calmodulin-stimulated functions:I Our results demonstrate that trifluoperazine specifically blocks stimulation of water permeability by both vasopressin and cyclic AMP, suggesting a post-cyclic AMP site of action. Consistent with this, we found that trifluoperazine did not inhibit cyclic AMP-dependent kinase activity in the bladder. In addition, we found that the number of vasopressininduced intramembranous particle aggregates was markedly decreased by trifluoperazine. These data suggest that the most significant site of calciumcalmodulin interaction occurs somewhere between kinase activation and aggre-