Pacemaker activity in the insect (T. molitor) heart: role of the sarcoplasmic reticulum

Abstract

The electrophysiological properties of the myogenic cardiac cells of insects have been analyzed, but the mechanisms that regulate the pacemaker activity have not been elucidated yet. In mammalian pacemaker cells, different types of membrane ion channels seem to be sequentially activated, perhaps in a cooperative fashion with the current generated by Ca(2+) extrusion mediated by the electrogenic Na(+)/Ca(2+) exchanger, which is sustained by the diastolic sarcoplasmic reticulum (SR) Ca(2+) release. The objective of the present work was to investigate the role of the SR function on the basal beating rate (BR), and BR modulation by extracellular Ca(2+) concentration ([Ca(2+)](o)) and neurotransmitters in the in situ dorsal vessel (heart) of the mealworm beetle Tenebrio molitor. The main observations were as follows: 1) basal BR was reduced by 50% by inhibition of SR function, but not affected by perfusion with CsCl or ZD7288; 2) spontaneous activity was abolished by Cd(2+); 3) a robust positive chronotropic response could be elicited to serotonin (5-HT), but not to norepinephrine or carbamylcholine; 4) SR inhibition abolished the sustained chronotropic stimulation by [Ca(2+)](o) elevation and by 5-HT, while the latter was unaffected by CsCl. It is concluded that, in T. molitor heart, BR is markedly, but not exclusively, dependent on the SR function, and that BR control and modulation by both [Ca(2+)](o) and 5-HT requires a functional SR.

Heart mechanical and hemodynamic parameters of a beetle, Tenebrio molitor, at selected ages

“…Our study demonstrated that older beetles had more abnormalities, like arrhythmia, in heart rhythm, which was constant from posterior to anterior (registered by visual observations). This regular rhythm was also observed in previous studies of T. molitor heart physiology (Feliciano, Bassani, Olivieira, & Bassani, ; Markou & Theophilidis, ). In T. molitor , the spontaneous electrical activity always originates at the most posterior cardiac segment and travels to the most anterior region of the dorsal vessel (Markou & Theophilidis, ).…”

Biological activity of Melia azedarach extracts against Spodoptera exigua

“…The heartbeat frequency measured in the S. exigua pupae was significantly decreased after topical application of both tested extracts. Proper functioning of the heart is one of the major physiological processes essential for normal functioning of the insect organism (Feliciano et al 2011). Even slight alterations in the heart functioning may interrupt the homeostasis and cause severe changes (Piazza & Wessells 2011).…”

Limulus and heart rhythm

“…In insect Tenebrio molitor , a mealworm beetle, application of 5 mM 2,3‐butanedione monoxime (BDM) for 2 min significantly decreases the mechanical activity of the heart, whereas no effects on electrogram were observed (Feliciano, Bassani, Oliveira, & Bassani, ). They have used low‐impedance suction microelectrodes made of glass in contrast to a flexible small diameter plastic tube with a narrow end/opening that is fire polished to unfailingly achieve tight contacts (Kodirov, ).…”

“…They have used low‐impedance suction microelectrodes made of glass in contrast to a flexible small diameter plastic tube with a narrow end/opening that is fire polished to unfailingly achieve tight contacts (Kodirov, ). BDM almost obliterates the contraction within 10 min, but the electrical activity changes only in rate and amplitude (Feliciano et al, ). The depolarizing and repolarizing polarity distribution of electrograms also differ compared with the control.…”

“…However, 100 μM Cd 2+ completely and reversibly diminishes both parameters. The HR was Ca 2+ and concentration dependent, although the effects started to saturate around 4 mM (Feliciano et al, ). The HR was similarly slowed (~60 vs. 30 beats min −1 ) in the presence of 2,5‐tert‐butyl‐4,5 hydroquinone (BHQ), ryanodine, and thapsigargin, respectively.…”