The effects of cyanide on intracellular ionic exchange in ferret and rat ventricular myocardium

Abstract

The effects of cyanide on Ca 2+ exchange in isolated ventricular myocytes and on the intracellular concentrations of Ca 2+ , Na + and H + have been investigated to assess the contribution that mitochondria might play in cellular Ca 2+ metabolism. Ionic levels were measured with ion-selective electrodes. KCN (2.5 mM) inhibited a component of Ca 2+ exchange in myocytes that could be attributed to mitochondrial exchange, but was without effect on non-mitochondrial Ca 2+ exchange. NaCN (2.5 mM) caused a transient reduction of [H + ] i , [Na + ] i and [Ca 2+ ] i when applied to the superfusate bathing ventricular trabeculae or papillary muscles. The transient changes of [Na + ] i were accentuated when the preparation was exposed to a solution which would be expected to increase the cellular calcium content. The reduction of [Na + ] i which accompanies a reduction of the extracellular sodium concentration, [Na] o , was attenuated in the presence of NaCN, but the intracellular acidosis resulting from a reduction of [Na] o was unaffected by NaCN. A small, but significant, rise of [Ca 2+ ] i accompanied a reduction of [Na] o but only when NaCN was present in the superfusate. It is concluded that cyanide ions have a reasonably specific action on cardiac cellular ionic metabolism. Its primary action is to prevent mitochondrial Ca 2+ sequestration. It is postulated that a Na + /H + exchange, possibly at the sarcolemma, could account for some of the changes to sarcoplasmic ionic levels observed. In a solution of low [Na] o , it is concluded that mitochondria could sequester at least 30% of the calcium accumulated by the cell even though the sarcoplasmic [Ca 2+ ] does not exceed 0.3 μM.

Analysis and presentation of intracellular measurements obtained with ion‐selective microelectrodes

“…The majority of results obtained with ion-selective microelectrodes (ISEs) and analysed here have been summarized elsewhere: Na+-ISE (Chapman et al 1983;Fry, Harding & Mounsey, 1987); H+-ISE (Blatter & McGuigan, 1989); Mg2+-ISE (Fry, 1986a, cardiac muscle;Blatter, 1989, skeletal muscle); Ca2+-ISE (Fry et al 1987). These measurements have been supplemented by unpublished material and were obtained from ferret and guinea-pig ventricular myocardium at 22-25°C (Bern) and 37°C (London) and also from frog skeletal muscle (Rochester).…”

Interaction of intracellular ion buffering with transmembrane-coupled ion transport.

“…However, total cell calcium may be as large as 6-40 mmol/liter ICS during experimental interventions designed to load Ca ++ (Bridge and Bassingthwaighte, 1983;Murphy et al, 1983;Langer, 1964;Carafoli, 1973;Chapman et al, 1983;Fry et al, 1984aFry et al, , 1987. Most of this calcium is held in mitochondria which have a substantial reversible buffering capacity (Carafoli, 1973).…”

“…The lowest buffer value represents rapidly reversible buffering seen during physiologically normal circumstances (1-5 mmol/ liter ICS; Langer, 1964Langer, , 1974Bridge, 1986;Fintel and Langer, 1986). The next largest value represents an average estimate for intact cells during nonphysiologic experimental interventions, such as high doses of glycosides (Bridge and Bassingthwaighte, 1983;Murphy et al, 1983), reduced [Na]o (Langer, 1964;Carafoli, 1973;Chapman et al, 1983), or application of permeabilizing agents (Fry et al, 1984a(Fry et al, , 1987. This intermediate range of values (6-40 mmol/liter ICS) is primarily mitochondrial buffering.…”

Na–Picotransporter type I activity causes a transient intracellular alkalinization during ATP depletion in rabbit medullary thick ascending limb cells

“…Rat MTAL cells possess a large amount of PCr (approaching that of the brain) (Takeda et al 1994). However, in contrast to myocardial cells where ATP content starts to decline only after PCr concentration has dropped dramatically (Fry et al 1987), in rat MTAL cells PCr and ATP concentration decrease in parallel (Bastin et al 1987). Since PCr breakdown will only alkalinize the cells as long as ATP levels remain elevated and since ATP concentration declines very rapidly in these primary cultures (even before the onset of the alkalinization) it can be concluded that the alkalinization observed is not the result of PCr breakdown.…”

“…However, some reports on (transient) alkalinizations during ATP depletion have been published previously. During ischemia in muscle and myocardial cells, phosphocreatine (PCr) breakdown usually results in a transient alkalinization at the onset of ischemia (Allen et al 1985;Eisner et al 1989;Fry et al 1987;Kemp et al 2001). PCr is a high-energy phosphate donor and plays an important role not only in muscle contraction but also in buffering intracellular energy storage.…”