Camp. f3io&m. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA fhysiol. Vol. 96C, No. I, pp. 105-109, 1990 Printed in Great Britain 0306~4492/90 53.00 + 0.00 0 1990 Pergamon Press plc EFFECTS OF SODIUM AZIDE ON THE PORICHTHYS ISOLATED LUMINOUS ORGANS J. MALLEFET,* J. F. F&ES and F. BACUET Laboratoire de Physiologie GBnCrale et des Animaux Domestiques, Universite Catholique de Louvain, 5 place de la Croix du Sud, B-1348 Louvain-la-Neuve, Belgium. Telephone: (010) 473476 (Received 24 January 1990) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP Abstract-l. Application of sodium azide 10e3 M on isolated luminous organ of the epipelagic fish Porichrhy s always induced a light emission. 2. Although the parameters of azide luminescence were similar to those of the potassium cyanide induced luminescence, the metabolic mechanisms associated with this light emission appear to be different. 3. Effectively, neither glucose nor pyruvate showed inhibitory effects on the azide induced luminescence, although glucose totally suppressed KCN induced luminescence. 4. Further, contrary to the potassium cyanide luminescence, there is no important increase in the oxygen consumption during azide photogenesis. 5. Different hypotheses are discussed to explain azide induced luminescence. INTRODUCTION Isolated photophores of the epipelagic fish Porichthys produce a large luminescence when exposed to pot- assium cyanide (KCN), suggesting that the light production is under the control of an energy depen- dent inhibitory mechanism (Baguet, 1975; Mallefet and Baguet, 1984; Rees and Baguet, 1989). As glucose but not pyruvate inhibits this lumines- cence, KCN is assumed to inhibit specifically the cellular respiration inducing the luminescence of the photocytes (Rees and Baguet, 1988; Mallefet and Baguet, 1989a). In this new experimental series, we investigate the effects of sodium azide (NaN,), another respiratory chain inhibitor, on the isolated photophores of Porichthys. The results show that, although the induction of luminescence is similar to that observed upon cyanide application, the oxidative phosphorylations should not be the exclusive target of sodium azide. MATERIALS AND METHODS Dissection qf the phosphores Seven specimens of the midshipman fish Porichthys myr- iuster and notatus shipped by Pacific Bio-Marine Labora- tories (Venice, California) were kept in aquaria provided with aerated and UV sterilized running seawater (18°C). After anaesthesia with quinaldine (0.037% v/v) in sea- water (Allen and Sills, 1973), a strip of photophores from the mandibular, gular. branchial, ventral and pleural regions (using Greene’s terminology, 1899) was excised and im- mersed in saline. Experimental procedures Two different installations were used to study the effects of sodium azide on isolated photophores: when solely the light emission was measured, we utilized the experimental installation previously described (Rees and Baguet, 1988). *Charge de Recherches FNRS. When luminescence and oxygen consumption were simul- taneously recorded, photophores were laid as in the exper- imental set-up described previously by Mallefet and Baguet (1988). Solutions Potassium cyanide, sodium azide, glucose and pyruvate were purchased from Merck. They were dissolved in buffered Young’s saline (Young, 1933) containing (in mmol 1-r): NaCI, 150; KCI, 7.5; CaCl,, 3.5; MgCl,, 2.4; pH = 7.3 with Tris-HCI, 20, just prior to use. RESULTS 1. Luminescence On application of 10m4 M NaN,, isolated photo- phores never produced light. At the concentration of lo-) M, NaN, always induced the luminescence of the photophore (n = 38). The parameters of the light production are summarized in Table 1. Azide luminescence started 79.2 f 7.4 set after stimulation (LT) and reached a maximum value of 1554.4 f 275.8 Mq/sec (L,,,,,.) after 112 If: 7.7 set (TL,,,). Half-extinction time of luminescence (ER) was esti- mated at 263.6 f 22.5 sec. As azide and cyanide block the cellular respiration at the same level, the cytochrome aa, (Nicholls and Kimelberg, 1972), we have compared the light emis- sion triggered by these two metabolic inhibitors (lO-3 M). The time courses of the luminescences induced by 10m3 M KCN and NaN, were similar; neither the maximal light amplitude for KCN nor for NaN, were different, corresponding respectively to 4781 & 763 Mq/sec and 4824 rf: 697 Mq/sec (n = 6). As tt has been shown that glucose rather than pyruvate inhibits the KCN induced luminescence, we tested the effect of both substrates on the azide induced luminescence. Examination of Fig. 1 shows that neither glucose nor pyruvate significantly modified any parameters of the azide light pro- duction, although glucose totally suppressed the 105