Intracellular [Ca2+] and Vo2 after manipulation of the free-energy of the Na+/Ca(2+)-exchanger in isolated rat ventricular myocytes.
We have investigated whether the Na+/Ca(2+)-exchanger has a functional regulatory role in the control of oxidative metabolism in suspensions of isolated rat ventricular myocytes. Therefore we simultaneously measured intracellular [Ca2+] ([Ca2+]i) with Indo-1 and respiratory rate (Vo2) after abrupt manipulation of the free-energy of the Na+/Ca(2+)-exchanger (delta Gexch). The average fraction of viable myocytes was about 90% (82% rod-shaped plus 8% viable round cells). delta Gexch was manipulated either by an abrupt decrease of [Na+]o (in combination with an increase of [K+]o or [Ca2+]o) or by changing membrane potential and/or intracellular cation activities with the use of gramicidin or veratridine. A change of extracellular cation composition caused a transient increase of [Ca2+]i and Vo2, with peak values after 30 to 40 s and a new steady state near control values after 180 to 240 s. Peak values of the transients were associated with the magnitude of the thermodynamic disturbance. Inhibition of sodium-pump activity with ouabain greatly enhanced peak values and reduced the rate of return to a new steady state. Reversal of the initial disturbance of delta Gexch by restoring [Na+]o or reduction of [Ca2+]o during the time course of the transients greatly accelerated return to a new steady-state. An increase of sarcolemmal sodium permeability with the Na-channel ligand veratridine or manipulation of [Na+]i and [K+]i with the Na+/K(+)-exchanger gramicidin caused monophasic increase of both [Ca2+]i and Vo2. The relationship between VO2 and [Ca2+]i was the same, irrespective of the nature of the intervention (either extracellular or intracellular manipulation of delta Gexch). We conclude that cytoplasmic [Ca2+] (thermodynamically controlled by the Na+/Ca(2+)-exchanger) is a major regulator of the respiratory rate in (quiescent) myocytes.
Department of Clinical and Experimental Cardiology, Academic Medical Center, University of Amsterdam, The Netherlands.
J W
JW
Fiolet
A
A
Baartscheer
C A
CA
Schumacher
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D005456:Fluorescent Dyes; D006352:Heart Ventricles; D066298:In Vitro Techniques; D007211:Indoles; D007700:Kinetics; D008297:Male; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger; D013997:Time Factors
D002352:Carrier Proteins; D005456:Fluorescent Dyes; D007211:Indoles; D019831:Sodium-Calcium Exchanger; D010042:Ouabain; D012964:Sodium; C048960:indo-1; D002118:Calcium