QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by SMITH, P. J. S. Articles by HILL, R. B. Search for Related Content PubMed Articles by SMITH, P. J. S. Articles by HILL, R. B.

Journal of Experimental Biology 123,243-253 (1986)
Published by Company of Biologists 1986

Cardiac Performance in Response to Loading Pressures and Perfusion with 5-Hydroxytryptamine in the Isolated Heart of Busycon Canaliculatum (Gastropoda, Prosobranchia)

P. J. S. SMITH ¹ and R. B. HILL ²

¹ Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
² Department of Zoology, Rhode Island, RI02881, USA

In this study the effects of a molluscan neurotransmitter, 5-hydroxytryptamine (5-HT), were examined on the isolated and pumping heart of the gastropod mollusc Busycon canaliculatum. Unlike in previous studies, the response was measured in such a way as to equate it with cardiac output. In addition, the effects on the myogram form and the manner of perfusate ejection were also examined.

As would be expected from previous studies, 5-HT affects heart rate, showing a positive chronotropic response at a threshold of around 10^-9 moll^-1. Stroke volume shows little evidence of being regulated by 5-HT concentration. This observation was unexpected as 5-HT is commonly reported to regulate the ‘force’ of contraction in a molluscan heart and, at constant perfusion conditions, this might have been expected to find expression as an increase in stroke volume. 5-HT does, however, have a very clear dose-dependent effect on the aortic pressure pulse amplitude and duration. Amplitude increases markedly (250%) over the concentrations used (10^-10-10^-6moll^-1) with a threshold around 10^-8 moll^-1 The effect on the duration has the same threshold but the opposite result, with a reduction to approximately 50% of the original value. The same amount of perfusate is therefore being ejected at a higher pressure and flow rate. It is suggested that this might have important implications for a soft-bodied animal with a hydrostatic skeleton.

The electrical activity of the heart was also examined and showed that 5-HT increased the amplitude of both the spike and plateau phase of the action potential. The duration of the latter was reduced. This is discussed with reference to other studies.

Key words: loading pressure, heart, 5-hydeoxytryptamine, Mollusca

Submitted on February 3, 1986