A comparative study of the role of mitochondria and the sarcoplasmic reticulum in the uptake and release of Ca⁺⁺ by the rat diaphragm

Abstract

The respective importance of mitochondria and of sarcoplasmic reticulum in the uptake and maintenance of C a + + by the isolated rat diaphragm has been compared. Diaphragms were incubated a t 30" in conditions optimal for Ca++ uptake either by isolated mitochondria or by sarcoplasmic reticulum: more Ca++ was taken up from the "mitochondrial" medium. For maximal uptake, Pi and Mg++ were necessary; substitution of NaCl and KCI with sucrose had no effect on the uptake. The uptake was markedly inhibited by uncouplers of oxidative phosphorylation, by respiratory inhibitors, and by lowering the temperature of the incubation medium to 0"; it was not affected by oligomycin, aurovertin, DCCD, nor by inhibitors of Ca+ + transport in the isolated sarcoplasmic reticulum (ergotamine, ergobasinine, caffeine). The lack of effect of caffeine was not due to lack of penetration into the muscle. Permeability barriers for ergotamine and ergobasinine could not be excluded. The maintenance of Ca++ by the diaphragm was optimal in a medium containing Pi and Mg+ +. Uncoupling agents and respiratory inhibitors accelerated the rate and extent of release of Ca++ by the diaphragm. Lowering the temperature of the incubation medium to O", or addition of oligomycin, aurovertin, DCCD, had no effect on the release. The release of C a + + was also unaffected by ergotamine, ergobasinine, caffeine. The results suggest a role for mitochondria in the uptake and maintenance of Ca+ + by the isolated diaphragm.

Actions of dinitrophenol and some other metabolic inhibitors on cortical neurones

“…An important effect of DNP and other uncouplers (or inhibitors) of oxidative phosphorylation is to slow down the mitochondrial accumulation of Ca2+, the mechanism by which the intracellular Ca2+ concentration is normally kept at a very low level (Lehninger et al 1967;Carafoli, Patriarca & Rossi, 1969;Caswell, 1969;Glagoleva, Liberman & Khashaev, 1970;Lust & Robinson, 1970). Uncouplers and possibly other metabolic inhibitors may thus produce a rapid rise in cytoplasmic-free Ca2+.…”

Association of mitochondria with the plasma membrane of the acinar cells of the mouse submaxillary glands

“…An energy-requiring calcium transport also occurs in mitochondria [Lehninger et al, 1967], The close association of mitochondria with the plasma membrane of acinar cells may indicate that these mitochondria are regulating intra- cellular calcium concentration [Carafoli et al, 1969],…”

Properties of the fragmented sarcoplasmic reticulum from fast twitch and slow twitch muscles

“…Received for publication 6 August 1970 and in revised form 9 November 1970. and others (7) doubted that FSR of slow twitch muscles plays the same dominant role in relaxation as it does in fast twitch muscle.…”

“…The role of the sarcoplasmic reticulum (SR) in the relaxation of white, fast twitch skeletal muscle is well accepted (1,2), but there is no agreement (3)(4)(5)(6)(7) about the importance of the SR in slow twitch muscles, e.g., the soleus of the rabbit (8) or guinea pig (9). Studies from this group have recently established that fast twitch muscles may be red both by gross inspection and by histochemical techniques (9).…”