The role of proctolin in the antenna-heart beat acceleration of Periplaneta americana (L.).
So-called accessorial pulsatile circulatory organs in insects have developed during evolutionary reduction of the vascular system. As such a peripheral organ, the antenna-heart supplies the antennae with haemolymph. In the antenna-heart, the beat rhythm is generated by a myogenic automatism and is controlled neuronally. The electrical stimulation of the antenna-heart nerve produces an immediate heart beat inhibition brought about by octopamine release. Following this heart inhibition, an accelerating effect can be observed, which is based on a peptidergic mechanism. Proctolin-like material was found in both the dilator muscle and the antenna-heart nerve by means of immunocytochemistry. After HPLC-separation of antenna-heart tissue, proctolin was identified by sequencing the bioactive material and subsequent mass spectrometry. Proctolin proved to be extraordinarily effective producing stimulation of the antenna-heart beat rate up to 450%. The threshold concentration is 10(-10) mol.1(-1) and the value of the dissociation constant was fixed to KO = 1.3 x 10(-8) mol.1(-1). The chrono-trophic effect is caused by an increase in the steepness of the rising phase of pacemaker activity. The enhancement of the membrane resistance Rinput indicates a reduction of K(+)-conductance by proctolin. The PI-second messenger system is involved as well. Proctolin was identified and isolated from a real target organ. This fact and the physiological results furnished proof of peptidergic transmitter function of proctolin in the antenna-heart.
Hertel
W
W
Institut für Allgemeine Zoologie und Tierphysiologie, Friedrich-Schiller-Universität Jena, Germany.
Richter
M
M
Rapus
J
J
Eckert
M
M
Penzlin
H
H
D000818:Animals; D002320:Cardiovascular Physiological Phenomena; D002319:Cardiovascular System / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D007150:Immunohistochemistry; D007447:Invertebrate Hormones / Q000302:isolation & purification / Q000494:pharmacology / Q000502:physiology; D008297:Male; D009479:Neuropeptides; D018377:Neurotransmitter Agents / Q000302:isolation & purification / Q000494:pharmacology / Q000502:physiology*; D009842:Oligopeptides / Q000302:isolation & purification / Q000494:pharmacology / Q000502:physiology*; D010526:Periplaneta / Q000502:physiology*
D007447:Invertebrate Hormones; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D009842:Oligopeptides; C011536:proctolin