Heartbeat patterns during the postembryonic development of Drosophila melanogaster

Pulsations of the dorsal vessel were recorded in vivo during the whole postembryonic development of D. melanogaster, by means of a newly invented, pulse-light opto-cardiographic method. The young larvae of the 1st and 2nd instars submerged in the feeding medium exhibited extremely high rates of heartbeat, 7 Hz at room temperature. These values are among the highest rates of heartbeat ever recorded in the animal kingdom. The fully grown larvae of the 3rd instar showed approximately half of the maximum heartbeat rate (3.5–4 Hz), which became stabilized after pupariation to 2.5–2.7 Hz.The larval heartbeat was always uni-directional, in the forward-oriented or anterograde direction and it was almost continuous. The slowly disintegrating, old larval heart used to beat at the constant frequency of 2.5–2.7 Hz until complete cessation of all cardiac functions in 1-day-old puparium. In spite of the persisting constant heartbeat frequency, the transformation process of the larval heart was associated with successively decreasing amplitude of the systolic contractions and with the prolongation of the resting periods. The newly formed heart of the pupal–adult structure exhibited a qualitatively new pattern of heartbeat activity, which was manifested by periodic reversal of the heartbeat with the faster anterograde and slower retrograde phases. The frequencies of both of these reciprocal cardiac pulsations gradually increased during the advanced pharate adult period, reaching the values of 4–5 Hz at the time of adult eclosion. Adult males and females also exhibited a perfect pattern of heartbeat reversal, with still very high rates of the anterograde heartbeat, in the range of 5–6 Hz. In addition to the cardiac functions, we have recorded several kinds of extracardiac pulsations, which often interfered severely with the recordings of the heartbeat. There were strong, irregular extracardiac pulsations of a neurogenic nature (somatic muscles, oral armature) and relatively slow extracardiac pulsations of a myogenic nature (intestinal peristaltics, 0.2–0.3 Hz). The extracardiac and cardiac pulsations were independent, their functions were not correlated. A possibility of creating new challenges in combination of molecular biology with the functional physiology of the heart have been discussed.