Heart rate and temperature in the snail Megalobulimus sanctipauli: role of the cardiac nerve.
The effects of five levels of temperature (15, 20, 25, 30, and 35 degrees C) on the heart rate of Megalobulimus sanctipauli were determined in a group of intact snails (n = 8). The results indicate that heart rate increased almost linearly with temperature over the tested range. The average Q10 calculated for the 15 to 25 degrees C range (1.9) did not differ from that calculated for the 25 to 35 degrees C range (1.7). To investigate the role of the cardiac nerve in mediating these heart rate alterations two others groups were tested: denervated animals (n = 8) and sham-operated control animals (n = 8). The results showed that the relationship between heart rate and each temperature level was not altered by cutting the visceral nerve that innervates the heart, indicating that the nervous system is not implicated in the increase in heart rate induced by increasing temperature. These changes in heart rate are probably due to a direct action of temperature on heart muscle by accelerating the myogenic self-excitation process.
Romero
S M
SM
Department of Biology, Faculty of Philosophy, Sciences and Letters of Ribeirão Preto, University of São Paulo, Brazil.
Hoffmann
A
A
D000818:Animals; D003080:Cold Temperature / Q000009:adverse effects; D006321:Heart / Q000294:innervation; D006339:Heart Rate / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects; D012908:Snails / Q000502:physiology*; D013696:Temperature